Chapter I: Part 1

Transcriber's notes:

(1) Numbers following letters (without space) like C2 were originally
printed in subscript. Letter subscripts are preceded by an
underscore, like C_n.

(2) Characters following a carat (^) were printed in superscript.

(3) Side-notes were relocated to function as titles of their respective
paragraphs.

(4) Letters topped by Macron are represented as [=x].

(5) dP stands for the partial-derivative symbol, or curled 'd'.

(6) [oo] stands for the infinity symbol, and [int] for the integral
symbol.

(7) The following typographical errors have been corrected:

Article DIAMOND: "If this be so the form of the diamond is really
the tetrahedron (and the various figures derived symmetrically from
it) and not the octahedron". 'octahedron' amended from
'octadehron'.

Article DIARY: "diaries began to be largely written in England,
although in most cases without any idea of even eventual
publication". 'largely' amended from 'largly'.

Article DICOTYLEDONS: "The arrangement of the conducting tissue in
the stem is characteristic; a transverse section of the very young
stem shows a number of distinct conducting strands". 'number'
amended from 'nunber'.

Article DIEKIRCH: "It remained more or less fortified until the
beginning of the 19th century when the French during their
occupation levelled the old walls, and substituted the avenues of
trees that now encircle the town". 'or' amended from 'for'.

Article DIFFERENCES, CALCULUS OF: "as the second difference of u_n,
and therefore as corresponding to the value x_n"; 'difference'
amended from 'dfference'.

Article DINAJPUR: "a town (with a population in 1901 of 13,430) and
district of British India, in the Rajshahi division of Eastern
Bengal and Assam". 'British' amended from 'Britsh'.

ENCYCLOPAEDIA BRITANNICA

A DICTIONARY OF ARTS, SCIENCES, LITERATURE
AND GENERAL INFORMATION

ELEVENTH EDITION

VOLUME VIII, SLICE IV

Diameter to Dinarchus

ARTICLES IN THIS SLICE:

DIAMETER DIEDENHOFEN
DIAMOND DIEKIRCH
DIAMOND NECKLACE, THE AFFAIR OF THE DIELECTRIC
DIANA DIELMANN, FREDERICK
DIANA MONKEY DIEMEN, ANTHONY VAN
DIANE DE FRANCE DIEPENBECK, ABRAHAM VAN
DIANE DE POITIERS DIEPPE
DIAPASON DIERX, LEON
DIAPER DIES, CHRISTOPH ALBERT
DIAPHORETICS DIEST
DIAPHRAGM DIESTERWEG, FRIEDRICH ADOLF WILHELM
DIARBEKR DIET
DIARRHOEA DIETARY
DIARY DIETETICS
DIASPORE DIETRICH, CHRISTIAN WILHELM ERNST
DIASTYLE DIETRICH OF BERN
DIATOMACEAE DIEZ, FRIEDRICH CHRISTIAN
DIAULOS DIEZ
DIAVOLO, FRA DIFFERENCES, CALCULUS OF
DIAZ, NARCISSE VIRGILIO DIFFERENTIAL EQUATION
DIAZ, PORFIRIO DIFFLUGIA
DIAZ DE NOVAES, BARTHOLOMEU DIFFRACTION OF LIGHT
DIAZO COMPOUNDS DIFFUSION
DIAZOMATA DIGBY, SIR EVERARD
DIBDIN, CHARLES DIGBY, SIR KENELM
DIBDIN, THOMAS FROGNALL DIGBY, KENELM HENRY
DIBDIN, THOMAS JOHN DIGENES ACRITAS, BASILIUS
DIBRA DIGEST
DIBRUGARH DIGESTIVE ORGANS
DICAEARCHUS DIGGES, WEST
DICE DIGIT
DICETO, RALPH DE DIGITALIS
DICEY, EDWARD DIGNE
DICHOTOMY DIGOIN
DICK, ROBERT DIJON
DICK, THOMAS DIKE
DICKENS, CHARLES JOHN HUFFAM DIKKA
DICKINSON, ANNA ELIZABETH DILAPIDATION
DICKINSON, JOHN DILATATION
DICKSON, SIR ALEXANDER DILATORY
DICKSON, SIR JAMES ROBERT DILEMMA
DICOTYLEDONS DILETTANTE
DICTATOR DILIGENCE
DICTIONARY DILKE, SIR CHARLES WENTWORTH
DICTYOGENS DILL
DICTYS CRETENSIS DILLEN, JOHANN JAKOB
DICUIL DILLENBURG
DIDACHE, THE DILLENS, JULIEN
DIDACTIC POETRY DILLINGEN
DIDEROT, DENIS DILLMANN, CHRISTIAN AUGUST
DIDIUS SALVIUS JULIANUS, MARCUS DILLON, ARTHUR RICHARD
DIDO DILLON, JOHN
DIDON, HENRI DILUVIUM
DIDOT DIME
DIDRON, ADOLPHE NAPOLEON DIMENSION
DIDYMI DIMITY
DIDYMIUM DINAJPUR
DIDYMUS DINAN
DIDYMUS CHALCENTERUS DINANT
DIE (town of France) DINAPUR
DIE (datum) DINARCHUS
DIEBITSCH, HANS KARL FRIEDRICH ANTON

DIAMETER (from the Gr. [Greek: dia], through, [Greek: metron], measure), in geometry, a line passing through the centre of a circle or conic section and terminated by the curve; the "principal diameters" of the ellipse and hyperbola coincide with the "axes" and are at right angles; "conjugate diameters" are such that each bisects chords parallel to the other. The diameter of a quadric surface is a line at the extremities of which the tangent planes are parallel. Newton defined the diameter of a curve of any order as the locus of the centres of the mean distances of the points of intersection of a system of parallel chords with the curve; this locus may be shown to be a straight line. The word is also used as a unit of linear measurement of the magnifying power of a lens or microscope.

In architecture, the term is used to express the measure of the lower part of the shaft of a column. It is employed by Vitruvius (iii. 2) to determine the height of a column, which should vary from eight to ten diameters according to the intercolumniation: and it is generally the custom to fix the lower diameter of the shaft by the height required and the Order employed. Thus the diameter of the Roman Doric should be about one-eighth of the height, that of the Ionic one-ninth, and of the Corinthian one-tenth (see ORDER).

DIAMOND, a mineral universally recognized as chief among precious stones; it is the hardest, the most imperishable, and also the most brilliant of minerals.[1] These qualities alone have made it supreme as a jewel since early times, and yet the real brilliancy of the stone is not displayed until it has been faceted by the art of the lapidary (q.v.); and this was scarcely developed before the year 1746. The consummate hardness of the diamond, in spite of its high price, has made it most useful for purposes of grinding, polishing and drilling. Numerous attempts have been made to manufacture the diamond by artificial means, and these attempts have a high scientific interest on account of the mystery which surrounds the natural origin of this remarkable mineral. Its physical and chemical properties have been the subject of much study, and have a special interest in view of the extraordinary difference between the physical characters of the diamond and those of graphite (blacklead) or charcoal, with which it is chemically identical, and into which it can be converted by the action of heat or electricity. Again, on account of the great value of the diamond, much of the romance of precious stones has centred round this mineral; and the history of some of the great diamonds of historic times has been traced through many extraordinary vicissitudes.

The name [Greek: Adamas], "the invincible," was probably applied by the Greeks to hard metals, and thence to corundum (emery) and other hard stones. According to Charles William King, the first undoubted application of the name to the diamond is found in Manilius (A.D. 16),--_Sic Adamas_, _punctum lapidis_, _pretiosior auro_,--and Pliny (A.D. 100) speaks of the rarity of the stone, "the most valuable of gems, known only to kings." Pliny described six varieties, among which the Indian, having six pointed angles, and also resembling two pyramids (_turbines_, whip-tops) placed base to base, may probably be identified as the ordinary octahedral crystal (fig. 1). The "diamond" (_Yahalom_) in the breastplate of the high priest (Ex. xxxix. 11) was certainly some other stone, for it bore the name of a tribe, and methods of engraving the true diamond cannot have been known so early. The stone can hardly have become familiar to the Romans until introduced from India, where it was probably mined at a very early period. But one or other of the remaining varieties mentioned by Pliny (the Macedonian, the Arabian, the Cyprian, &c.) may be the true diamond, which was in great request for the tool of the gem-engraver. Later Roman authors mentioned various rivers in India as yielding the _Adamas_ among their sands. The name _Adamas_ became corrupted into the forms _adamant_, _diamaunt_, _diamant_, _diamond_; but the same word, owing to a medieval misinterpretation which derived it from _adamare_ (compare the French word _aimant_), was also applied to the lodestone.

Like all the precious stones, the diamond was credited with many marvellous virtues; among others the power of averting insanity, and of rendering poison harmless; and in the middle ages it was known as the "pietra della reconciliazione," as the peacemaker between husband and wife.

_Scientific Characters._--The majority of minerals are found most commonly in masses which can with difficulty be recognized as aggregates of crystalline grains, and occur comparatively seldom as distinct crystals; but the diamond is almost always found in single crystals, which show no signs of previous attachment to any matrix; the stones were, until the discovery of the South African mines, almost entirely derived from sands or gravels, but owing to the hardness of the mineral it is rarely, if ever, water-worn, and the crystals are often very perfect. The crystals belong to the cubic system, generally assuming the form of the octahedron (fig. 1), but they may, in accordance with the principles of crystallography, also occur in other forms symmetrically derived from the octahedron,--for example, the cube, the 12-faced figure known as the rhombic dodecahedron (fig. 2), or the 48-faced figure known as the hexakis-octahedron (fig. 3), or in combinations of these. The octahedron faces are usually smooth; most of the other faces are rounded (fig. 4). The cube faces are rough with protruding points. The cube is sometimes found in Brazil, but is very rare among the S. African stones; and the dodecahedron is perhaps more common in Brazil than elsewhere. There is often a furrow running along the edges of the octahedron, or across the edges of the cube, and this indicates that the apparently simple crystal may really consist of eight individuals meeting at the centre; or, what comes to the same thing, of two individuals interpenetrating and projecting through each other. If this be so the form of the diamond is really the tetrahedron (and the various figures derived symmetrically from it) and not the octahedron. Fig. 5 shows how the octahedron with furrowed edge may be constructed from two interpenetrating tetrahedra (shown in dotted lines). If the grooves be left out of account, the large faces which have replaced each tetrahedron corner then make up a figure which has the aspect of a simple octahedron. Such regular interpenetrations are known in crystallography as "twins." There are also twins of diamond in which two octahedra (fig. 6) are united by contact along a surface parallel to an octahedron face without interpenetration. On account of their resemblance to the twins of the mineral spinel (which crystallizes in octahedra) these are known as "spinel twins." They are generally flattened along the plane of union. The crystals often display triangular markings, either elevations or pits, upon the octahedron faces; the latter are particularly well defined and have the form of equilateral triangles (fig. 7). They are similar to the "etched figures" produced by moistening an octahedron of alum, and have probably been produced, like them, by the action of some solvent. Similar, but somewhat different markings are produced by the combustion of diamond in oxygen, unaccompanied by any rounding of the edges.

Diamond possesses a brilliant "adamantine" lustre, but this tends to be greasy on the surface of the natural stones and gives the rounded crystals somewhat the appearance of drops of gum. Absolutely colourless stones are not so common as cloudy and faintly coloured specimens; the usual tints are grey, brown, yellow or white; and as rarities, red, green, blue and black stones have been found. The colour can sometimes be removed or changed at a high temperature, but generally returns on cooling. It is therefore more probably due to metallic oxides than to hydrocarbons. Sir William Crookes has, however, changed a pale yellow diamond to a bluish-green colour by keeping it embedded in radium bromide for eleven weeks. The black coloration upon the surface produced by this process, as also by the electric bombardment in a vacuum tube, appears to be due to a conversion of the surface film into graphite. Diamond may break with a conchoidal fracture, but the crystals always cleave readily along planes parallel to the octahedron faces: of this property the diamond cutters avail themselves when reducing the stone to the most convenient form for cutting; a sawing process, has, however, now been introduced, which is preferable to that of cleavage. It is the hardest known substance (though tantalum, or an alloy of tantalum now competes with it) and is chosen as 10 in the mineralogist's scale of hardness; but the difference in hardness between diamond (10) and corundum (9) is really greater than that between corundum (9) and talc (1); there is a difference in the hardness of the different faces; the Borneo stones are also said to be harder than those of Australia, and the Australian harder than the African, but this is by no means certain. The specific gravity ranges from 3.56 to 3.50, generally about 3.52. The coefficient of expansion increases very rapidly above 750 deg., and diminishes very rapidly at low temperatures; the maximum density is attained about -42 deg. C.

The very high refractive power (index = 2.417 for sodium light) gives the stone its extraordinary brilliancy; for light incident within a diamond at a greater angle than 24-1/2 deg. is reflected back into the stone instead of passing through it; the corresponding angle for glass is 40-1/2 deg. The very high dispersion (index for red light = 2.402, for blue light = 2.460) gives it the wonderful "fire" or display of spectral colours. Certain absorption bands at the blue end of the spectrum are supposed to be due to rare elements such as samarium. Unlike other cubic crystals, diamond experiences a diminution of refractive index with increase of temperature. It is very transparent for Rontgen rays, whereas paste imitations are opaque. It is a good conductor of heat, and therefore feels colder to the touch than glass and imitation stones. The diamond has also a somewhat greasy feel. The specific heat increases rapidly with rising temperature up to 60 deg. C., and then more slowly. Crystals belonging to the cubic system should not be birefringent unless strained; diamond often displays double refraction particularly in the neighbourhood of inclusions, both liquid and solid; this is probably due to strain, and the spontaneous explosion of diamonds has often been observed. Diamond differs from graphite in being a bad conductor of electricity: it becomes positively electrified by friction. The electrical resistance is about that of ordinary glass, and is diminished by one-half during exposure by Rontgen rays; the dielectric constant (16) is greater than that which should correspond to the specific gravity.

The phosphorescence produced by friction has been known since the time of Robert Boyle (1663); the diamond becomes luminous in a dark room after exposure to sunlight or in the presence of radium; and many stones phosphoresce beautifully (generally with a pale green light) when subjected to the electric discharge in a vacuum tube. Some diamonds are more phosphorescent than others, and different faces of a crystal may display different tints. The combustibility of the diamond was predicted by Sir Isaac Newton on account of its high refractive power; it was first established experimentally by the Florentine Academicians in 1694. In oxygen or air diamond burns at about 850 deg., and only continues to do so if maintained at a high temperature; but in the absence of oxidising agents it may be raised to a much higher temperature. It is, however, infusible at the temperature of the electric arc, but becomes converted superficially into graphite. Experiments on the combustion of diamond were made by Smithson Tennant (1797) and Sir Humphry Davy (1816), with the object of proving that it is pure carbon; they showed that burnt in oxygen it yields exactly the same amount of carbon dioxide as that produced by burning the same weight of carbon. Still more convincing experiments were made by A. Krause in 1890. Similarly Guyton de Morveau showed that, like charcoal, diamond converts soft iron into steel. Diamond is insoluble in acid and alkalis, but is oxidised on heating with potassium bichromate and sulphuric acid.

Bort (or Boart) is the name given to impure crystals or fragments useless for jewels; it is also applied to the rounded crystalline aggregates, which generally have a grey colour, a rough surface, often a radial structure, and are devoid of good cleavage. They are sometimes spherical ("shot bort"). Carbonado or "black diamond," found in Bahia (also recently in Minas Geraes), is a black material with a minutely crystalline structure somewhat porous, opaque, resembling charcoal in appearance, devoid of cleavage, rather harder than diamond, but of less specific gravity; it sometimes displays a rude cubic crystalline form. The largest specimen found (1895) weighed 3078 carats. Both bort and carbonado seem to be really aggregates of crystallized diamond, but the carbonado is so nearly structureless that it was till recently regarded as an amorphous modification of carbon.

_Uses of the Diamond._--The use of the diamond for other purposes than jewelry depends upon its extreme hardness: it has always been the only material used for cutting or engraving the diamond itself. The employment of powdered bort and the lapidary's wheel for faceting diamonds was introduced by L. von Berquen of Bruges in 1476. Diamonds are now employed not only for faceting precious stones, but also for cutting and drilling glass, porcelain, &c,; for fine engraving such as scales; in dentistry for drilling; as a turning tool for electric-light carbons, hard rubber, &c.; and occasionally for finishing accurate turning work such as the axle of a transit instrument. For these tools the stone is actually shaped to the best form: it is now electroplated before being set in its metal mount in order to secure a firm fastening. It is also used for bearings in watches and electric meters. The best glaziers' diamonds are chosen from crystals such that a natural curved edge can be used. For rock drills, and revolving saws for stone cutting, either diamond, bort or carbonado is employed, set in steel tubes, disks or bands. Rock drilling is the most important industrial application; and for this, owing to its freedom from cleavage, the carbonado is more highly prized than diamond; it is broken into fragments about 3 carats in weight; and in 1905 the value of carbonado was no less than from L10 to L14 a carat. It has been found that the "carbons" in drills can safely be subjected to a pressure of over 60 kilograms per square millimetre, and a speed of 25 metres per second. A recent application of the diamond is for wire drawing; a hole tapering towards the centre is drilled through a diamond, and the metal is drawn through this. No other tool is so endurable, or gives such uniform thickness of wire.

_Distribution and Mining._--The most important localities for diamonds have been: (1) India, where they were mined from the earliest times till the close of the 19th century; (2) South America, where they have been mined since the middle of the 18th century; and (3) South Africa, to which almost the whole of the diamond-mining industry has been transferred since 1870.

_India._--The diamond is here found in ancient sandstones and
conglomerates, and in the river gravels and sands derived from them.
The sandstones and conglomerates belong to the Vindhyan formation and
overlie the old crystalline rocks: the diamantiferous beds are well
defined, often not more than 1 ft. in thickness, and contain pebbles
of quartzite, jasper, sandstone, slate, &c. The mines fall into five
groups situated on the eastern side of the Deccan plateau about the
following places (beginning from the south), the first three being in
Madras. (1) Chennur near Cuddapah on the river Pennar. (2) Kurnool
near Baneganapalle between the rivers Pennar and Kistna. (3) Kollar
near Bezwada on the river Kistna. (4) Sambalpur on the river Mahanadi
in the Central Provinces. (5) Panna near Allahabad, in Bundelkhand.
The mining has always been carried on by natives of low caste, and by
primitive methods which do not differ much from those described by the
French merchant Jean Baptiste Tavernier (1605-1689), who paid a
prolonged visit to most of the mines between 1638 and 1665 as a
dealer in precious stones. According to his description shallow pits
were sunk, and the gravel excavated was gathered into a walled
enclosure where it was crushed and water was poured over it, and it
was finally sifted in baskets and sorted by hand. The buying and
selling was at that period conducted by young children. In more modern
times there has been the same excavation of shallow pits, and
sluicing, sifting and sorting, by hand labour, the only machinery used
being chain pumps made of earthen bowls to remove the water from the
deeper pits.

At some of the Indian localities spasmodic mining has been carried on
at different periods for centuries, at some the work which had been
long abandoned was revived in recent times, at others it has long been
abandoned altogether. Many of the large stones of antiquity were
probably found in the Kollar group, where Tavernier found 60,000
workers in 1645 (?), the mines having, according to native accounts,
been discovered about 100 years previously. Golconda was the fortress
and the market for the diamond industry at this group of mines, and so
gave its name to them. The old mines have now been completely
abandoned, but in 1891 about 1000 carats were being raised annually in
the neighbourhood of Hyderabad. The Sambalpur group appear to have
been the most ancient mines of all, but they were not worked later
than 1850. The Panna group were the most productive during the 19th
century. India was no doubt the source of all the large stones of
antiquity; a stone of 67-3/8 carats was found at Wajra Karur in the
Chennur group in 1881, and one of 210-1/2 carats at Hira Khund in 1809.
Other Indian localities besides those mentioned above are Simla, in
the N.W. Provinces, where a few stones have been found, and a district
on the Gouel and the Sunk rivers in Bengal, which V. Ball has
identified with the Soumelpour mentioned by Tavernier. The mines of
Golconda and Kurnool were described as early as 1677 in the twelfth
volume of the _Philosophical Transactions_ of the Royal Society. At
the present time very few Indian diamonds find their way out of the
country, and, so far as the world's supply is concerned, Indian mining
of diamonds may be considered extinct. The first blow to this industry
was the discovery of the Brazilian mines in Minas Geraes and Bahia.

_Brazil._---Diamonds were found about 1725 at Tejuco (now Diamantina)
in Minas Geraes, and the mining became important about 1740. The chief
districts in Minas Geraes are (1) Bagagem on the W. side of the Serra
da Mata da Corda; (2) Rio Abaete on the E. side of the same range;
these two districts being among the head waters of the Rio de San
Francisco and its tributaries; (3) Diamantina, on and about the
watershed separating the Rio de San Francisco from the Rio
Jequitinhonha; and (4) Grao Mogul, nearly 200 m. to the N.E. of
Diamantina on the latter river.

The Rio Abaete district was worked on a considerable scale between
1785 and 1807, but is now abandoned. Diamantina is at present the most
important district; it occupies a mountainous plateau, and the
diamonds are found both on the plateau and in the river valleys below
it. The mountains consist here of an ancient laminated micaceous
quartzite, which is in parts a flexible sandstone known as
itacolumite, and in parts a conglomerate; it is interbedded with
clay-slate, mica-schist, hornblende-schist and haematite-schist, and
intersected by veins of quartz. This series is overlain unconformably
by a younger quartzite of similar character, and itself rests upon the
crystalline schists. The diamond is found under three conditions: (1)
in the gravels of the present rivers, embedded in a ferruginous
clay-cemented conglomerate known as _cascalho_; (2) in terraces
(gupiarras) in a similar conglomerate occupying higher levels in the
present valleys; (3) in plateau deposits in a coarse surface
conglomerate known as _gurgulho_, the diamond and other heavy minerals
being embedded in the red clay which cements the larger blocks. Under
all these three conditions the diamond is associated with fragments of
the rocks of the country and the minerals derived from them,
especially quartz, hornstone, jasper, the polymorphous oxide of
titanium (rutile, anatase and brookite), oxides and hydrates of iron
(magnetite, ilmenite, haematite, limonite), oxide of tin, iron
pyrites, tourmaline, garnet, xenotime, monazite, kyanite, diaspore,
sphene, topaz, and several phosphates, and also gold. Since the heavy
minerals of the _cascalho_ in the river beds are more worn than those
of the terraces, it is highly probable that they have been derived by
the cutting down of the older river gravels represented by the
terraces; and since in both deposits the heavy minerals are more
abundant near the heads of the valleys in the plateau, it is also
highly probable that both have really been derived from the plateau
deposit. In the latter, especially at Sao Joao da Chapada, the
minerals accompanying the diamond are scarcely worn at all; in the
terraces and the river beds they are more worn and more abundant; the
terraces, therefore, are to be regarded as a first concentration of
the plateau material by the old rivers; and the _cascalho_ as a second
concentration by the modern rivers. The mining is carried on by
negroes under the supervision of overseers; the _cascalho_ is dug out
in the dry season and removed to a higher level, and is afterwards
washed out by hand in running water in shallow wooden basins
(_bateas_). The terraces can be worked at all seasons, and the
material is partly washed out by leading streams on to it. The washing
of the plateau material is effected in reservoirs of rain water.

It is difficult to obtain an estimate of the actual production of the
Minas Geraes mines, for no official returns have been published, but
in recent years it has certainly been rivalled by the yield in Bahia.
The diamond here occurs in river gravels and sands associated with
the same minerals as in Minas Geraes; since 1844 the richest mines
have been worked in the Serra de Cincora, where the mountains are
intersected by the river Paraguassu and its tributaries; it is said
that there were as many as 20,000 miners working here in 1845, and it
was estimated that 54,000 carats were produced in Bahia in 1858. The
earlier workings were in the Serra de Chapada to the N.W. of the mines
just mentioned. In 1901 there were about 5000 negroes employed in the
Bahia mines; methods were still primitive; the _cascalho_ was dug out
from the river beds or tunnelled out from the valley side, and washed
once a week in sluices of running water, where it was turned over with
the hoe, and finally washed in wooden basins and picked over by hand;
sometimes also the diamantiferous material is scooped out of the bed
of the shallow rivers by divers, and by men working under water in
caissons. It is almost exclusively in the mines of Bahia, and in
particular in the Cincora district, that the valuable carbonado is
found. The carbonado and the diamond have been traced to an extensive
hard conglomerate which occurs in the middle of the sandstone
formation. Diamonds are also mined at Salobro on the river Pardo not
far inland from the port of Canavieras in the S.E. corner of Bahia.
The enormous development of the South African mines, which supplied in
1906, about 90% of the world's produce, has thrown into the shade the
Brazilian production; but the _Bulletin_ for Feb. 1909 of the
International Bureau of American Republics gave a very confident
account of its future, under improved methods.

_South Africa._---The first discovery was made in 1867 by Dr W. G.
Atherstone, who identified as diamond a pebble obtained from a child
in a farm on the banks of the Orange river and brought by a trader to
Grahamstown; it was bought for L500 and displayed in the Paris
Exhibition of that year. In 1869 a stone weighing 83-1/2 carats was
found near the Orange river; this was purchased by the earl of Dudley
for L25,000 and became famous as the "Star of South Africa." A rush of
prospectors at once took place to the banks of the Orange and Vaal
rivers, and resulted in considerable discoveries, so that in 1870
there was a mining camp of no less than 10,000 persons on the "River
Diggings." In the River Diggings the mining was carried on in the
coarse river gravels, and by the methods of the Brazilian negroes and
of gold placer-miners. A diggers' committee limited the size of claims
to 30 ft. square, with free access to the river bank; the gravel and
sand were washed in cradles provided with screens of perforated metal,
and the concentrates were sorted by hand on tables by means of an iron
scraper.

But towards the close of 1870 stones were found at Jagersfontein and
at Dutoitspan, far from the Vaal river, and led to a second great rush
of prospectors, especially to Dutoitspan, and in 1871 to what is now
the Kimberley mine in the neighbourhood of the latter. At each of
these spots the diamantiferous area was a roughly circular patch of
considerable size, and in some occupied the position of one of those
depressions or "pans" so frequent in S. Africa. These "dry diggings"
were therefore at first supposed to be alluvial in origin like the
river gravels; but it was soon discovered that, below the red surface
soil and the underlying calcareous deposit, diamonds were also found
in a layer of yellowish clay about 50 ft. thick known as "yellow
ground." Below this again was a hard bluish-green serpentinous rock
which was at first supposed to be barren bed-rock; but this also
contained the precious stone, and has become famous, under the name of
"blue ground," as the matrix of the S. African diamonds. The yellow
ground is merely decomposed blue ground. In the Kimberley district
five of these round patches of blue ground were found within an area
little more than 3 m. in diameter; that at Kimberley occupying 10
acres, that at Dutoitspan 23 acres. There were soon 50,000 workers on
this field, the canvas camp was replaced by a town of brick and iron
surrounded by the wooden huts of the natives, and Kimberley became an
important centre.

It was soon found that each mine was in reality a huge vertical funnel
or crater descending to an unknown depth, and filled with
diamantiferous blue ground. At first each claim was an independent pit
31 ft. square sunk into the blue ground; the diamantiferous rock was
hoisted by bucket and windlass, and roadways were left across the pit
to provide access to the claims. But the roadways soon fell in, and
ultimately haulage from the claims could only be provided by means of
a vast system of wire ropes extending from a triple staging of
windlasses erected round the entire edge of the mine, which had by
this time become a huge open pit; the ropes from the upper windlasses
extended to the centre, and those from the lower tier to the sides of
the pit; covering the whole mass like a gigantic cobweb. (See Plate
II. fig. 12.) The buckets of blue ground were hauled up these ropes by
means of horse whims, and in 1875 steam winding engines began to be
employed. By this time also improved methods in the treatment of the
blue ground were introduced. It was carried off in carts to open
spaces, where an exposure of some weeks to the air was found to
pulverize the hard rock far more efficiently than the old method of
crushing with mallets. The placer-miner's cradle and rocking-trough
were replaced by puddling troughs stirred by a revolving comb worked
by horse power; reservoirs were constructed for the scanty
water-supply, bucket elevators were introduced to carry away the
tailings; and the natives were confined in compounds. For these
improvements co-operation was necessary; the better claims, which in
1872 had risen from L100 to more than L4000 in value, began to be
consolidated, and a Mining Board was introduced.

PLATE I.

PLATE II.

In a very few years, however, the open pit mining was rendered
impossible by the mud rushes, by the falls of the masses of barren
rock known as "reef," which were left standing in the mine, and by
landslips from the sides, so that in 1883, when the pit had reached a
depth of about 400 ft., mining in the Kimberley crater had become
almost impossible. By 1889, in the whole group of mines, Kimberley,
Dutoitspan, De Beers and Bultfontein, open pit working was practically
abandoned. Meanwhile mining below the bottom of the pits by means of
shafts and underground tunnels had been commenced; but the full
development of modern methods dates from the year 1889 when Cecil
Rhodes and Alfred Beit, who had already secured control of the De
Beers mine, acquired also the control of the Kimberley mine, and
shortly afterwards consolidated the entire group in the hands of the
De Beers Company. (See KIMBERLEY.)

The scene of native mining was now transferred from the open pit to
underground tunnels; the vast network of wire ropes (Plate II. fig.
12) with their ascending and descending buckets disappeared, and with
it the cosmopolitan crowd of busy miners working like ants at the
bottom of the pit. In place of all this, the visitor to Kimberley
encounters at the edge of the town only a huge crater, silent and
apparently deserted, with no visible sign of the great mining
operations which are conducted nearly half a mile below the surface.
The aspect of the Kimberley pit in 1906 is shown in fig. 13 of Plate
II., which may be compared with the section of fig. 8.

In fig. 13, Plate II., the sequence of the basalt, shale and melaphyre
is clearly visible on the sides of the pit; and fig. 8 shows how the
crater or "pipe" of blue ground has penetrated these rocks and also
the underlying quartzite. The workings at De Beers had extended into
the still more deeply seated granite in 1906. Figure 9, Plate I.,
shows the top of the De Beers' crater with basalt overlying the shale.
Figure 8 also explains the modern system of mining introduced by
Gardner Williams. A vertical shaft is sunk in the vicinity of the
mine, and from this horizontal tunnels are driven into the pipe at
different levels separated by intervals of 40 ft. Through the blue
ground itself on each level a series of parallel tunnels about 120 ft.
apart are driven to the opposite side of the pipe, and at right angles
to these, and 36 ft. apart, another series of tunnels. When the
tunnels reach the side of the mine they are opened upwards and
sideways so as to form a large chamber, and the overlying mass of blue
ground and debris is allowed to settle down and fill up the gallery.
On each level this process is carried somewhat farther back than on
the level below (fig. 8); material is thus continually withdrawn from
one side of the mine and extracted by means of the rock shaft on the
opposite side, while the superincumbent debris is continually sinking,
and is allowed to fall deeper on the side farthest from the shaft as
the blue ground is withdrawn from beneath it. In 1905 the main shaft
had been sunk to a depth of 2600 ft. at the Kimberley mine.

For the extraction and treatment of the blue ground the De Beers
Company in its great winding and washing plant employs labour-saving
machinery on a gigantic scale. The ground is transferred in trucks to
the shaft where it is automatically tipped into skips holding 96 cubic
ft. (six truck loads); these are rapidly hoisted to the surface, where
their contents are automatically dumped into side-tipping trucks, and
these in turn are drawn away in a continual procession by an endless
wire rope along the tram lines leading to the vast "distributing
floors." These are open tracts upon which the blue ground is spread
out and left exposed to sun and rain until it crumbles and
disintegrates, the process being hastened by harrowing with steam
ploughs; this may require a period of three or six months, or even a
year. The stock of blue ground on the floors at one time in 1905 was
nearly 4,500,000 loads. The disintegrated ground is then brought back
in the trucks and fed through perforated cylinders into the washing
pans; the hard blue which has resisted disintegration on the floors,
and the lumps which are too big to pass the cylindrical sieves, are
crushed before going to the pans. These are shallow cylindrical
troughs containing muddy water in which the diamonds and other heavy
minerals (concentrates) are swept to the rim by revolving toothed
arms, while the lighter stuff escapes near the centre of the pan. The
concentrates are then passed over sloping tables (pulsator) and shaken
to and fro under a stream of water which effects a second
concentration of the heaviest material.

Until recently the final separation of the diamond from the
concentrates was made by hand picking, but even this has now been
replaced by machinery, owing to the remarkable discovery that a
greased surface will hold a diamond while allowing the other heavy
minerals to pass over it. The concentrates are washed down a sloping
table of corrugated iron which is smeared with grease, and it is found
that practically all the diamonds adhere to the table, and the other
minerals are washed away. At the large and important Premier mine in
the Transvaal the Elmore process, used in British Columbia and in
Wales for the separation of metallic ores, has been also introduced.
In the Elmore process oil is employed to float off the materials which
adhere to it, while the other materials remain in the water, the oil
being separated from the water by centrifugal action. The other
minerals found in the concentrates are pebbles and fragments of
pyrope, zircon, cyanite, chrome-diopside, enstatite, a green pyroxene,
mica, ilmenite, magnetite, chromite, hornblende, olivine, barytes,
calcite and pyrites.

In all the S. African mines the diamonds are not only crystals of
various weights from fractions of a carat to 150 carats, but also
occur as microscopic crystals disseminated through the blue ground. In
spite of this, however, the average yield in the profitable mines is
only from 0.2 carat to 0.6 carat per load of 1600 lb., or on an
average about 1-1/2 grs. per ton. The annual output of diamonds from
the De Beers mines was valued in 1906 at nearly L5,000,000; the value
per carat ranging from about 35s. to 70s.

From Gardner Williams's _Diamond Mines of South Africa_. FIG. 8.]

Pipes similar to those which surround Kimberley have been found in
other parts of S. Africa. One of the best known is that of
Jagersfontein, which was really the first of the dry diggings
(discovered in 1870). This large mine is near Fauresmith and 80 m. to
the south of Kimberley. In 1905 the year's production from the Orange
River Colony mines was more than 320,000 carats, valued at L938,000.
But by far the largest of all the pipes hitherto discovered is the
Premier mine in the Transvaal, about 300 m. to the east of Kimberley.
This was discovered in 1902 and occupies an area of about 75 acres. In
1906 it was being worked as a shallow open mine; but the description
of the Kimberley methods given above is applicable to the washing
plant at that time being introduced into the Premier mine upon a very
large scale. Comparatively few of the pipes which have been discovered
are at all rich in diamonds, and many are quite barren; some are
filled with "hard blue" which even if diamantiferous may be too
expensive to work.

The most competent S. African geologists believe all these remarkable
pipes to be connected with volcanic outbursts which occurred over the
whole of S. Africa during the Cretaceous period (after the deposition
of the Stormberg beds), and drilled these enormous craters through all
the later formations. With the true pipes are associated dykes and
fissures also filled with diamantiferous blue ground. It is only in
the more northerly part of the country that the pipes are filled with
blue ground (or "kimberlite"), and that they are diamantiferous; but
over a great part of Cape Colony have been discovered what are
probably similar pipes filled with agglomerates, breccias and tuffs,
and some with basic lavas; one, in particular, in the Riversdale
Division near the southern coast, being occupied by a melilite-basalt.
It is quite clear that the occurrence of the diamond in the S. African
pipes is quite different from the occurrences in alluvial deposits
which have been described above. The question of the origin of the
diamond in S. Africa and elsewhere is discussed below.

The River Diggings on the Vaal river are still worked upon a small
scale, but the production from this source is so limited that they are
of little account in comparison with the mines in the blue ground. The
stones, however, are good; since they differ somewhat from the
Kimberley crystals it is probable that they were not derived from the
present pipes. Another S. African locality must be mentioned;
considerable finds were reported in 1905 and 1906 from gravels at
Somabula near Gwelo in Rhodesia where the diamond is associated with
chrysoberyl, corundum (both sapphire and ruby), topaz, garnet,
ilmenite, staurolite, rutile, with pebbles of quartz, granite,
chlorite-schist, &c. Diamond has also been reported from kimberlite
"pipes" in Rhodesia.

_Other Localities._--In addition to the South American localities
mentioned above, small diamonds have also been mined since their
discovery in 1890 on the river Mazaruni in British Guiana, and finds
have been reported in the gold washings of Dutch Guiana. Borneo has
possessed a diamond industry since the island was first settled by the
Malays; the references in the works of Garcia de Orta, Linschoten, De
Boot, De Laet and others, to Malacca as a locality relate to Borneo.
The large Borneo stone, over 360 carats in weight, known as the Matan,
is in all probability not a diamond. The chief mines are situated on
the river Kapuas in the west and near Bandjarmassin in the south-east
of the island, and the alluvial deposits in which they occur are
worked by a small number of Chinese and Malays. Australia has yielded
diamonds in alluvial deposits near Bathurst (where the first discovery
was made in 1851) and Mudgee in New South Wales, and also near Bingara
and Inverell in the north of the colony. At Mount Werong a stone
weighing 29 carats was found in 1905. At Ruby Hill near Bingara they
were found in a breccia filling a volcanic pipe. At Ballina, in New
England, diamonds have been found in the sea sand. Other Australian
localities are Echunga in South Australia; Beechworth, Arena and
Melbourne in Victoria; Freemantle and Nullagine in Western Australia;
the Palmer and Gilbert rivers in Queensland. These have been for the
most part discoveries in alluvial deposits of the goldfields, and the
stones were small. In Tasmania also diamonds have been found in the
Corinna goldfields. Europe has produced few diamonds. Humboldt
searched for them in the Urals on account of the similarity of the
gold and platinum deposits to those of Brazil, and small diamonds were
ultimately found (1829) in the gold washings of Bissersk, and later at
Ekaterinburg and other spots in the Urals. In Lapland they have been
found in the sands of the Pasevig river. Siberia has yielded isolated
diamonds from the gold washings of Yenisei. In North America a few
small stones have been found in alluvial deposits, mostly auriferous,
in Georgia, N. and S. Carolina, Kentucky, Virginia, Tennessee,
Wisconsin, California, Oregon and Indiana. A crystal weighing 23-3/4
carats was found in Virginia in 1855, and one of 21-1/4 carats in
Wisconsin in 1886. In 1906 a number of small diamonds were discovered
in an altered peridotite somewhat resembling the S. African blue
ground, at Murfreesboro, Pike county, Arkansas. Considerable interest
attaches to the diamonds found in Wisconsin, Michigan and Ohio near
the Great Lakes, for they are here found in the terminal moraines of
the great glacial sheet which is supposed to have spread southwards
from the region of Hudson Bay; several of the drift minerals of the
diamantiferous region of Indiana have been identified as probably of
Canadian origin; no diamonds have however yet been found in the
intervening country of Ontario. A rock similar to the blue ground of
Kimberley has been found in the states of Kentucky and New York. The
occurrence of diamond in meteorites is described below.

_Origin of the Diamond in Nature._--It appears from the foregoing
account that at most localities the diamond is found in alluvial
deposits probably far from the place where it originated. The minerals
associated with it do not afford much clue to the original conditions;
they are mostly heavy minerals derived from the neighbouring rocks, in
which the diamond itself has not been observed. Among the commonest
associates of the diamond are quartz, topaz, tourmaline, rutile,
zircon, magnetite, garnet, spinel and other minerals which are common
accessory constituents of granite, gneiss and the crystalline schists.
Gold (also platinum) is a not infrequent associate, but this may only
mean that the sands in which the diamond is found have been searched
because they were known to be auriferous; also that both gold and
diamond are among the most durable of minerals and may have survived
from ancient rocks of which other traces have been lost.

The localities at which the diamond has been supposed to occur in its
original matrix are the following:--at Wajra Karur, in the Cuddapah
district, India, M. Chaper found diamond with corundum in a decomposed
red pegmatite vein in gneiss. At S[=a]o Joao da Chapada, in Minas
Geraes, diamonds occur in a clay interstratified with the itacolumite,
and are accompanied by sharp crystals of rutile and haematite in the
neighbourhood of decomposed quartz veins which intersect the
itacolumite. It has been suggested that these three minerals were
originally formed in the quartz veins. In both these occurrences the
evidence is certainly not sufficient to establish the presence of an
original matrix. At Inverell in New South Wales a diamond (1906) has
been found embedded in a hornblende diabase which is described as a
dyke intersecting the granite. Finally there is the remarkable
occurrence in the blue ground of the African pipes.

There has been much controversy concerning the nature and origin of
the blue ground itself; and even granted that (as is generally
believed) the blue ground is a much serpentinized volcanic breccia
consisting originally of an olivine-bronzite-biotite rock (the
so-called kimberlite), it contains so many rounded and angular
fragments of various rocks and minerals that it is difficult to say
which of them may have belonged to the original rock, and whether any
were formed _in situ_, or were brought up from below as inclusions.
Carvill Lewis believed the blue ground to be true eruptive rock, and
the carbon to have been derived from the bituminous shales of which it
contains fragments. The Kimberley shales, which are penetrated by the
De Beers group of pipes, were, however, certainly not the source of
the carbon at the Premier (Transvaal) mine, for at this locality the
shales do not exist. The view that the diamond may have crystallized
out from solution in its present matrix receives some support from the
experiments of W. Luzi, who found that it can be corroded by the
solvent action of fused blue ground; from the experiments of J.
Friedlander, who obtained diamond by dissolving graphite in fused
olivine; and still more from the experiments of R. von Hasslinger and
J. Wolff, who have obtained it by dissolving graphite in a fused
mixture of silicates having approximately the composition of the blue
ground. E. Cohen, who regarded the pipes as of the nature of a mud
volcano, and the blue ground as a kimberlite breccia altered by
hydrothermal action, thought that the diamond and accompanying
minerals had been brought up from deep-seated crystalline schists.
Other authors have sought the origin of the diamond in the action of
the hydrated magnesian silicates on hydrocarbons derived from
bituminous schists, or in the decomposition of metallic carbides.

Of great scientific interest in this connexion is the discovery of
small diamonds in certain meteorites, both stones and irons; for
example, in the stone which fell at Novo-Urei in Penza, Russia, in
1886, in a stone found at Carcote in Chile, and in the iron found at
Canon Diablo in Arizona. Graphitic carbon in cubic form (cliftonite)
has also been found in certain meteoric "irons," for example in those
from Magura in Szepes county, Hungary, and Youndegin near York in
Western Australia. The latter is now generally believed to be altered
diamond. The fact that H. Moissan has produced the diamond
artificially, by allowing dissolved carbon to crystallize out at a
high temperature and pressure from molten iron, coupled with the
occurrence in meteoric iron, has led Sir William Crookes and others to
conclude that the mineral may have been derived from deep-seated iron
containing carbon in solution (see the article GEM, ARTIFICIAL). Adolf
Knop suggested that this may have first yielded hydrocarbons by
contact with water, and that from these the crystalline diamond has
been formed. The meteoric occurrence has even suggested the fanciful
notion that all diamonds were originally derived from meteorites. The
meteoric iron of Arizona, some of which contains diamond, is actually
found in and about a huge crater which is supposed by some to have
been formed by an immense meteorite penetrating the earth's crust.

It is, at any rate, established that carbon can crystallize as diamond
from solution in iron, and other metals; and it seems that high
temperature and pressure and the absence of oxidizing agents are
necessary conditions. The presence of sulphur, nickel, &c., in the
iron appears to favour the production of the diamond. On the other
hand, the occurrence in meteoric stones, and the experiments mentioned
above, show that the diamond may also crystallize from a basic magma,
capable of yielding some of the metallic oxides and ferro-magnesian
silicates; a magma, therefore, which is not devoid of oxygen. This is
still more forcibly suggested by the remarkable eclogite boulder found
in the blue ground of the Newlands mine, not far from the Vaal river,
and described by T. G. Bonney. The boulder is a crystalline rock
consisting of pyroxene (chrome-diopside), garnet, and a little
olivine, and is studded with diamond crystals; a portion of it is
preserved in the British Museum (Natural History). In another eclogite
boulder, diamond was found partly embedded in pyrope. Similar boulders
have also been found in the blue ground elsewhere. Specimens of pyrope
with attached or embedded diamond had previously been found in the
blue ground of the De Beers mines. In the Newlands boulder the
diamonds have the appearance of being an original constituent of the
eclogite. It seems therefore that a holocrystalline pyroxene-garnet
rock may be one source of the diamond found in blue ground. On the
other hand many tons of the somewhat similar eclogite in the De Beers
mine have been crushed and have not yielded diamond. Further, the
ilmenite, which is the most characteristic associate of the diamond in
blue ground, and other of the accompanying minerals, may have come
from basic rocks of a different nature.

The Inverell occurrence may prove to be another example of diamond
crystallized from a basic rock.

In both occurrences, however, there is still the possibility that the
eclogite or the basalt is not the original matrix, but may have caught
up the already formed diamond from some other matrix. Some regard the
eclogite boulders as derived from deep-seated crystalline rocks,
others as concretions in the blue ground.

None of the inclusions in the diamond gives any clue to its origin;
diamond itself has been found as an inclusion, as have also black
specks of some carbonaceous materials. Other black specks have been
identified as haematite and ilmenite; gold has also been found; other
included minerals recorded are rutile, topaz, quartz, pyrites,
apophyllite, and green scales of chlorite (?). Some of these are of
very doubtful identification; others (e.g. apophyllite and chlorite)
may have been introduced along cracks. Some of the fibrous inclusions
were identified by H. R. Goppert as vegetable structures and were
supposed to point to an organic origin, but this view is no longer
held. Liquid inclusions, some of which are certainly carbon dioxide,
have also been observed.

Finally, then, both experiment and the natural occurrence in rocks and
meteorites suggest that diamond may crystallize not only from iron but
also from a basic silicate magma, possibly from various rocks
consisting of basic silicates. The blue ground of S. Africa may be
the result of the serpentinization of several such rocks, and
although now both brecciated and serpentinized some of these may have
been the original matrix. A circumstance often mentioned in support of
this view is the fact that the diamonds in one pipe generally differ
somewhat in character from those of another, even though they be near
neighbours.

_History._--All the famous diamonds of antiquity must have been Indian stones. The first author who described the Indian mines at all fully was the Portuguese, Garcia de Orta (1565), who was physician to the viceroy of Goa. Before that time there were only legendary accounts like that of Sindbad's "Valley of the Diamonds," or the tale of the stones found in the brains of serpents. V. Ball thinks that the former legend originated in the Indian practice of sacrificing cattle to the evil spirits when a new mine is opened; birds of prey would naturally carry off the flesh, and might give rise to the tale of the eagles carrying diamonds adhering to the meat.

The following are some of the most famous diamonds of the world:--