PEARL, CORAL, AMBER
Although none of the substances considered in this chapter come within
the strict definition of a stone, since they are directly the result of
living agency, yet pearl at least cannot be denied the title of a gem.
Both pearl and coral contain calcium carbonate in one or other of its
crystallized forms, and both are gathered from the sea; but otherwise
they have nothing in common. Amber is of vegetable origin, and is a
very different substance.
PEARL
From that unrecorded day when some scantily clothed savage seeking for
succulent food opened an oyster and found to his astonishment within
its shell a delicate silvery pellet that shimmered in the light of a
tropical sun, down to the present day, without intermission, pearl has
held a place all its own in the rank of jewels. Though it be lacking in
durability, its beauty cannot be disputed, and large examples, perfect
in form and lustre, are sufficiently rare to tax the deepest purse.
The substance composing the pearl is identical with the iridescent
lining—mother-o’-pearl or nacre, as it is termed—of the shell.
Tortured by the intrusion of some living thing, a boring parasite,
a worm, or a small fish, or of a grain of sand or other inorganic
substance, and without means to free itself, the mollusc perforce
neutralizes the irritant matter by converting it into an object of
beauty that eventually finds its way into some jewellery cabinet. Built
up in a haphazard manner and not confined by the inexorable laws of
intermolecular action, a pearl may assume any and every variety of
shape from the regular to the fantastic. It may be truly spherical,
egg- or pear-shaped—pear-drops or pear-eyes, as they are termed—or it
may be quite irregular—the so-called baroque or barrok pearls. The
first is the most prized, but a well-shaped drop-pearl is in great
demand for pendants or ear-rings. The colour is ordinarily white, or
faintly tinged yellowish or bluish, and somewhat rarely, salmon-pink,
reddish, or blackish grey. Perfect black pearls are valuable, but not
as costly as the finest of the white. Though not transparent, pearl is
to a varying extent translucent, and its characteristic lustre—‘orient’
in the language of jewellery—is due to the same kind of interaction
of light reflected from different layers that has been remarked upon
in the case of opal and certain other stones. The translucency varies
in degree, and some jewellers speak of the ‘water’ of pearls just as
in the case of diamonds. If a pearl be sliced across the middle and
the section be examined under the microscope, it will be seen that
the structure consists of concentric shells and resembles that of an
onion. These shells are alternately composed of calcium carbonate in
its crystallized form, aragonite, and of a horny organic matter known
as conchiolin, and they evidently represent the result of intermittent
growth. Because of their composite character, pearls have a specific
gravity ranging from 2·65 to 2·69-2·84-2·89 in the case of pink
pearls—which is appreciably less than that of aragonite, 2·94: the
hardness is about the same, namely, 3½ to 4 on Mohs’s scale. That the
arrangement of the mineral layers is approximately parallel is evinced
by the distinctness of the shadow-edges shown on examination with the
refractometer. Pearls require very careful handling, both because they
are comparatively soft and therefore apt to be scratched, and because
they are chemically affected by acids, and even by the perspiration
from the skin. Acids attack only the calcium carbonate, not the
organic matter; the well-known story therefore of Cleopatra dissolving
a valuable pearl in vinegar, which is moreover, too weak an acid to
effect the solution quickly, must not be accepted too literally.
Pearls are not cut like stones, and therefore as soon as the precious
bloom has once gone, nothing can be done to revive it. Attempts are
sometimes made in the case of valuable pearls to remove the dull skin
and lay bare another iridescent layer underneath, but the operation is
exceedingly delicate. Even with the best of care pearls must in process
of time perish owing to the decay of the organic constituent. Pearls
that have been discovered in ancient tombs crumbled to dust at a touch,
and those formerly in ancient rings have vanished or only remain as
a brown powder, while the garnets or other stones set with them are
little the worse for the centuries that have passed by.
The largest known pearl was at one time in the famous collection
belonging to the banker, Henry Philip Hope. Cylindrical in form, with
a slight swelling at one end, it measures 50 mm. (2 inches) in length,
and 115 mm. (4½ inches) in circumference about the thicker, and 83
mm. (3¼ inches) about the thinner end, and weighs 454 carats. About
three-quarters of it is white in colour with a fine ‘orient,’ and the
remainder is bronze in tint. It is valued at upwards of £12,000. A
large pearl, 300 carats in weight, is in the imperial crown of the
Emperor of Austria, and another, pear-shaped, is in the possession of
the Shah of Persia. A beautiful white India pearl, a perfect sphere in
shape, and 28 carats in weight, is in the Museum of Zosima in Moscow;
it is known as ‘La Pellegrina.’ The ‘Great Southern Cross,’ which
consists of nine large pearls naturally joined together in the shape of
a cross, was discovered in an oyster fished up in 1886 off the beds of
Western Australia. The collection of jewels in the famous Green Vaults
at Dresden contains a number of pearls of curious shapes.
Large pearls are sold separately, while the small pearls known as
‘seed’ pearls come into the market bored and strung on silk in
‘bunches.’ The unit of weight is the pearl grain, which is a quarter
of a carat, and the rate of price depends on the square of the weight
in grains. The rate per unit or base varies from 6d. to 50s. according
to the shape and quality of the pearl. Spherical pearls command the
best prices, next the pearl-drops, and lastly the buttons; but whatever
the shape, it is imperative that the pearl have ‘orient,’ without which
it is valueless. The cheaper grades of pearls are sold by the carat.
[Illustration: _PLATE XXX_
NATIVES DRILLING PEARLS]
For use in necklaces and pendants pearls are bored with a steel drill,
and threaded with silk, an easy operation on account of their softness.
They harmonize well with diamonds. Small pearls are often set as a
frame to large coloured stones, to which they form an admirable foil.
Pearls set in rings or anywhere where the upper half alone would show
are generally sawn in halves; ‘button’ pearls find an extensive use in
modern rings.
Any mollusc, whether of the bi-valve or the uni-valve type, which
possesses a nacreous shell, has the power of producing pearls,
but only two, the pearl-oyster, _Meleagrina margaritifera_, and
the pearl-mussel, _Unio margarifer_, repay the cost of systematic
fishing. The outside of the shell is formed of the horny matter called
conchiolin; while the inside is composed of two coats, of which
the outer consists of alternate layers of conchiolin and calcium
carbonate in its crystallized form, calcite, and the inner of the same
organic matter, but with calcium carbonate in its other crystallized
form, aragonite. The latter coat forms the nacreous lining known as
mother-o’-pearl, which is identical in consistency with pearl, but
somewhat more transparent. The iridescence of mother-o’-pearl is due
not only to the fact that it is composed of a succession of thin
translucent layers, but also to the fact that these layers overlap
like slates on a house, and form a series of fine parallel lines on
the surface; diffraction therefore as well as interference of light
takes place, and a similar diffraction phenomenon is displayed even
by a cast of the inside of the shell. The animal has the property of
secreting calcium carbonate, which it absorbs from the sea-water, in
both its crystallized conditions as well as conchiolin. At the outer
rim it secretes conchiolin, further in calcite, and at the very inside
aragonite. The shape and appearance of a pearl therefore depend on
the position in which the intruding substance is situated within the
shell. The most perfect pearl has been in intermittent motion in the
interior of the mollusc, and has received successive coats according
to the position in which it happened to be. A parasite that bores
into the shell is walled up at the point of entrance, and a wart- or
blister-pearl results. The thinner the successive coats the finer
the lustre. Pearls have even been discovered embedded in the animal
itself. The number of pearls found in a shell depends on the number of
times the living host was compelled to seal up some irritant object,
and may vary from one up to the eighty-seven which are said to have
been found in an Indian oyster. That an oyster thus distinguished has
not led a happy existence is testified by the distorted shape of its
shell, a clue that guides the pearl-fishers in their search. Moreover,
pearl-oysters never have thick nacreous shells, and on the other hand
molluscs with fine mother-o’-pearl seldom contain pearls.
Beautiful white and silvery pearls are found in a small oyster that
lives at a depth of 6 to 13 fathoms (11-24 m.) in the Gulf of Manaar,
off the coast of Ceylon. About seven-eighths, however, of the pearls
that come into the market are obtained from a larger oyster which
has its home on the Arabian coast of the Persian Gulf. These famous
fisheries have been known since very early times. The pearls found
here are more yellowish than those from Ceylon, but are nevertheless
of excellent quality. The pearl fisheries off the north-west coast of
Western Australia and off Venezuela are also not unimportant, and fine
black pearls have been supplied by molluscs from the Gulf of Mexico.
[Illustration: _PLATE XXXI_
METAL FIGURES OF BUDDHA INSERTED IN A PEARL-OYSTER]
[Illustration: _PLATE XXXII_
FIG. 1
FIG. 2
SECTIONS OF CULTURE PEARL
FIG. 1. IN THE OYSTER. FIG. 2. WHEN FINISHED.
A. PEARLY DEPOSIT. B. PIECE OF MOTHER-O’-PEARL INSERTED IN THE OYSTER.
C. OUTER SHELL OF THE OYSTER. D. MOTHER-O’-PEARL BACK ADDED.]
The Chinese have long made a practice of introducing into the shell of
a pearl-oyster little tin images of Buddha in order that they may be
coated with the nacreous secretion. The Japanese have during recent
years made quite an industry of stimulating the efforts of the mollusc
by cementing small pieces of mother-o’-pearl to the interior surface
of the shell (Plate XXXII, Fig. 1); these ‘culture’ pearls, as they
are termed, are recognizable by examination of the back. About a year
has to elapse before a coating of a tenth of a millimetre is formed,
and another two years must pass before the thickness is doubled. After
removal the piece of mother-o’-pearl, which is now coated with several
nacreous layers, is cemented to a piece of ordinary mother-o’-pearl,
and the lower portion is ground to the usual symmetrical shape (Plate
XXXII, Fig. 2). Blister pearls are often similarly treated. In both
cases, however, the ‘orient’ is deficient in quality.
The finest mother-o’-pearl is supplied by a mollusc found in the sea
near the islands lying between Borneo and the Philippines, and fine
material is found at Shark Bay and off Thursday Island.
CORAL
Coral ranks far below pearl and meets with but limited appreciation.
It is common enough in warm seas, but the only kind which finds its
way into jewellery is the rose or red-coloured coral—the noble coral,
_Corallium nobile_ or _rubrum_. It consists of the axial skeleton of
the coral polyp, and is built up of hollow tubes fitting one within
the other. The composition is mainly calcium carbonate with a little
magnesium carbonate and a small amount of organic matter. The former
of the mineral substances is in the form of calcite, and the crystals
are arranged in fibrous form radiating at right angles to the axis of
the coral. The specific gravity varies from 2·6 to 2·7, being slightly
under that of calcite, and the hardness is somewhat greater, being
about 3¾ on Mohs’s scale.
The best red coral is found in the Mediterranean Sea off Algiers and
Tunis in Africa, and Sicily and the Calabrian Coast of Italy. The
industry of shaping and fashioning the coral is carried on almost
entirely in Italy. Coral is usually cut into beads, either round or
egg-shaped, and used for necklaces, rosaries, and bracelets. The best
quality fetches from 20s. to 30s. per carat.
AMBER
This fossil resin, yellow and brownish-yellow in tint, finds an
extensive use as the material for mouthpieces of pipes, cigar and
cigarette-holders, umbrella-handles, and so on, and is even locally
cut for jewellery, although its extreme softness, its hardness being
only 2½ on Mohs’s scale, quite unfits it for such a purpose. It is
only slightly denser than water, the specific gravity being about
1·10. Since the structure is amorphous the refraction is single, the
index being about 1·540. Amber, being a very bad conductor of heat, is
perceptibly warm to the touch. Its property of becoming electrified by
friction attracted early attention, and from the Greek name for it,
ἤλεκτρον, is derived our word electricity.
Amber is washed up by the sea off the coasts of Sicily and Prussia,
and of Norfolk and Suffolk in England. The finest examples, which are
picked up off the shore of Catania in Sicily, are distinguished by a
fine bluish fluorescence, resembling that seen in lubricating oil; such
pieces command good prices.
A recent resin, pale yellow in colour, known as kauri-gum, is found in
New Zealand, where it is highly valued.
TABLES
TABLE I
_Chemical Composition of Gem-Stones_
(_a_) ELEMENTS—
Diamond C
(_b_) OXIDES—
Corundum Al_{2}O_{3}
Quartz SiO_{2}
Chalcedony SiO_{2}
Opal SiO_{2}.nH_{2}O
(_c_) ALUMINATES—
Spinel MgAl_{2}O_{4}
Chrysoberyl BeAl_{2}O_{4}
(_d_) SILICATES—
Phenakite Be_{2}SiO_{4}
Dioptase H_{2}CuSiO_{4}
Peridot Mg_{2}SiO_{4}
Zircon ZrSiO_{4}
Enstatite MgSiO_{3}
Diopside CaMg(SiO_{3})_{2}
Nephrite CaMg_{3}(SiO_{3})_{4}
Sphene CaTiSiO_{5}
Benitoite BaTiSi_{3}O_{9}
Andalusite Al(AlO)SiO_{4}
Kyanite (AlO)_{2}SiO_{3}
Topaz [Al(F,OH)]_{2}SiO_{4}
Epidote Ca_{2}(Al,Fe)_{2}(AlOH)(SiO_{4})_{3}
Euclase Be(AlOH)SiO_{4}
Prehnite H_{2}Ca_{2}Al_{2}(SiO_{4})_{3}
Iolite H_{2}(Mg,Fe)_{4}Al_{8}Si_{10}O_{37}
{ Hessonite Ca_{3}Al_{2}(SiO_{4})_{3}
_Garnet_ { Pyrope Mg_{3}Al_{2}(SiO_{4})_{3}
{ Almandine Fe_{3}Al_{2}(SiO_{4})_{3}
{ Andradite Ca_{3}Fe_{2}(SiO_{4})_{3}
Beryl Be_{3}Al_{2}(SiO_{3})_{6}
Spodumene LiAl(SiO_{3})_{2}
Jadeite NaAl(SiO_{3})_{2}
Moonstone KAlSi_{3}O_{8}
Tourmaline{12SiO_{2}.3B_{2}O_{3}.(9-x)[(Al,Fe)_{2}O_{3}].3x[
{(Fe,Mn,Ca,Mg,K_{2},Na_{2},Li_{2},H_{2})O].3H_{2}O
Axinite HCa_{3}Al_{2}B(SiO_{4})_{4}
Idocrase (Ca,Mn,Mg,Fe)_{2}(Al,Fe)(OH,F)]Si_{2}O_{7}
(_e_) PHOSPHATES—
Beryllonite NaBePO_{4}
Apatite Ca_{5}(F,Cl)(PO_{4})_{3}
Turquoise CuOH.6[Al(OH)_{2}].H_{5}.(PO_{4})_{4}
TABLE II
_Colour of Gem-Stones_
_Colourless and White._—Diamond, corundum (white sapphire), topaz,
quartz (rock-crystal), zircon (when ‘fired’), moonstone; rarely
beryl, tourmaline; among the less common species, phenakite,
spodumene (colourless kunzite), beryllonite.
_Yellow._—Diamond, topaz, corundum (yellow sapphire), quartz
(citrine, Scotch or occidental topaz), tourmaline, zircon,
sphene, spodumene, beryl.
_Pink and Lilac._—Corundum (pink sapphire), spinel (balas-ruby),
tourmaline (rubellite), topaz (usually when ‘fired’), spodumene
(kunzite), beryl (morganite), quartz (rose-quartz).
_Red._—Corundum (ruby), garnet (pyrope, almandine), spinel
(balas-ruby), tourmaline (rubellite), zircon, opal (fire-opal).
_Green._—Beryl (emerald, aquamarine), peridot, corundum,
tourmaline, chrysoberyl (including alexandrite), zircon, garnet
(demantoid); among less common species, spodumene (hiddenite),
euclase, diopside, idocrase, epidote, apatite, obsidian; rarely
diamond; also semi-opaque, turquoise, jade.
_Blue._—Corundum (sapphire), spinel, topaz, tourmaline, zircon;
among the less common species, kyanite, iolite, benitoite,
apatite; rarely diamond; also semi-opaque, turquoise, lapis
lazuli, sodalite.
_Violet and Purple._—Quartz (amethyst), corundum (oriental
amethyst), spinel (almandine-spinel), garnet (almandine),
spodumene (kunzite), apatite.
_Brown._—Diamond, tourmaline, quartz (smoky-quartz); among the less
common species, andalusite, axinite, sphene.
TABLE III
_Refractive Indices of Gem-Stones_[8]
Opal 1·454
Moonstone 1·53 1·54
Iolite 1·543 1·551
Quartz 1·544 1·553
Beryllonite 1·553 1·565
Beryl 1·578 1·585
Turquoise 1·61 1·65
Topaz 1·618 1·627
Andalusite 1·632 1·643
Tourmaline 1·626 1·651
Apatite 1·642 1·646
Phenakite 1·652 1·667
Euclase 1·651 1·670
Spodumene 1·660 1·675
Enstatite 1·665 1·674
Peridot 1·659 1·697
Axinite 1·674 1·684
Diopside 1·685 1·705
Idocrase 1·714 1·719
Spinel 1·726
Kyanite 1·72 1·73
Epidote 1·735 1·766
Garnet (Hessonite) 1·745
Chrysoberyl 1·746 1·753
Garnet (Pyrope) 1·755
Benitoite 1·757 1·804
Corundum 1·761 1·770
Garnet (Almandine) 1·790
Zircon (a) 1·815
Garnet (Demantoid) 1·885
Sphene 1·901 1·985
Zircon (b) 1·927 1·980
Diamond 2·417
TABLE IV
_Colour-Dispersion of Gem-Stones_[9]
Moonstone ·012
Quartz ·013
Beryl ·014
Topaz ·014
Chrysoberyl ·015
Tourmaline ·017
Spodumene ·017
Corundum ·018
Peridot ·020
Spinel ·020
Garnet (Almandine) ·024
Garnet (Pyrope) ·027
Garnet (Hessonite) ·028
Zircon ·038
Diamond ·044
Sphene ·051
Garnet (Demantoid) ·057
TABLE V
_Character of the Refraction of Gem-Stones_
(_a_) SINGLE—
Diamond, spinel, garnet, opal.
Diamond and garnet frequently display local double refraction.
(_b_) UNIAXIAL, POSITIVE—
Quartz ·009
Phenakite ·015
Benitoite ·047
Zircon (b) ·053
Quartz exhibits circular polarization.
(_c_) UNIAXIAL, NEGATIVE—
Apatite ·004
Idocrase ·005
Beryl ·007
Corundum ·009
Tourmaline ·025
(_d_) BIAXIAL, POSITIVE—
Chrysoberyl ·007
Topaz ·009
Enstatite ·009
Spodumene ·015
Euclase ·019
Diopside ·020
Peridot ·038
Sphene ·084
(_e_) BIAXIAL, NEGATIVE—
Moonstone ·006
Iolite ·008
Axinite ·010
Andalusite ·011
Beryllonite ·012
Kyanite ·016
Epidote ·031
TABLE VI
_Dichroism of Gem-Stones_
(_a_) STRONG
Corundum, tourmaline, alexandrite, spodumene, andalusite, iolite,
epidote, axinite.
(_b_) DISTINCT
Emerald, topaz, quartz, peridot, chrysoberyl, enstatite, euclase,
idocrase, kyanite, sphene, apatite.
(_c_) WEAK
Beryl, diopside.
TABLE VII
_Specific Gravities of Gem-Stones_
Opal 2·15
Moonstone 2·57
Iolite 2·63
Quartz 2·66
Beryl 2·74
Turquoise 2·82
Beryllonite 2·84
Phenakite 2·99
Euclase 3·07
Tourmaline 3·10
Enstatite 3·10
Andalusite 3·18
Spodumene 3·18
Apatite 3·20
Axinite 3·28
Diopside 3·29
Epidote 3·37
Peridot 3·40
Idocrase 3·40
Sphene 3·40
Diamond 3·52
Topaz 3·53
Spinel 3·60
Kyanite 3·61
Garnet (Hessonite) 3·61
Benitoite 3·64
Chrysoberyl 3·73
Garnet (Pyrope) 3·78
Garnet (Demantoid) 3·84
Corundum 4·03
Garnet (Almandine) 4·05
Zircon (a) 4·20
Zircon (b) 4·69
TABLE VIII
_Degrees of Hardness of Gem-Stones_
5. Kyanite (5-7), apatite, lapis lazuli
5½. Enstatite, beryllonite, sphene
6. Opal, moonstone, turquoise, diopside
6½. Spodumene, peridot, garnet (demantoid), benitoite, idocrase,
epidote, axinite, jade (nephrite)
7. Iolite, quartz, tourmaline, jade (jadeite)
7¼. Garnet (hessonite, pyrope)
7½. Beryl, garnet (almandine), zircon, phenakite, euclase, andalusite
8. Topaz, spinel
8½. Chrysoberyl
9. Corundum
10. Diamond
TABLE IX.—DATA
_Densities of Water and Toluol at Ordinary Temperatures_
+-----------------------------+----------+----------+
| TEMPERATURE | WATER | TOLUOL |
+-----------------------------+----------+----------+
| Centigrade | Fahrenheit | | |
| | | | |
| 14° | 57·2° | 0·9994 | 0·8697 |
| 15° | 59·0° | 0·9992 | 0·8687 |
| 16° | 60·8° | 0·9990 | 0·8677 |
| 17° | 62·6° | 0·9988 | 0·8667 |
| 18° | 64·4° | 0·9986 | 0·8657 |
| 19° | 66·2° | 0·9985 | 0·8647 |
| 20° | 68·0° | 0·9983 | 0·8637 |
| 21° | 69·0° | 0·9981 | 0·8627 |
| 22° | 71·6° | 0·9979 | 0·8617 |
| 23° | 73·4° | 0·9977 | 0·8607 |
+-----------------------------+----------+----------+
1 English carat = 0·2053 gram
1 Metric carat = 0·2000 (one-fifth) gram
1 oz. Av. = 28·35 grams
1 lb. Av. = 0·4536 kilogram
1 inch = 25·4 millimetres
1 foot = 0·3048 metre
1 yard = 0·9144 metre
1 mile = 1·6093 kilometre
INDEX
Absorption, 53, 59
Absorption spectra, 59
Achroite, 220, 221
Adularia, 255
Agate, 247
Akbar Shah diamond, 163
Alalite, 272
Albite, 254
Alexandrite, 54, 60, 233
Scientific, 122
Almandine, 60, 214
Oriental, 112, 172
spinel, 112, 204
Amazon-stone, 255
Amber, 83, 298
Amethyst, 239, 242
Oriental, 111, 172, 239
Anatase, 281
Andalusite, 274
Andradite, 216
Anomalous refraction, 47
Anorthite, 254
Apatite, 279
Apophyllite, 290
Aquamarine, 184, 193
Arizona-ruby, 213
Artificial stones, 124
Asteria, 38, 177
Asterism, 38
Australia stones, 154, 174, 182, 195, 213, 216, 227, 232, 252,
288
Austrian Yellow diamond, 165
Aventurine, 240, 241
Axes, Crystallographic, 9
Optic, 49
Axinite, 278
Azure-quartz, 244
Azurite, 287
Balas-ruby, 203
Barnato, Barnett, 145
Baroque, Barrok, pearls, 292
Bastite, 272
Benitoite, 267
Berquem, Louis de, 90, 161
Beryl, 184
Beryllonite, 270
Bezel facet, 92
Biaxial double refraction, 45, 49, 57
Bisectrix, 45, 49
Black diamond, 129
Black lead, 129
Black opal, 249, 250
Black Prince’s ruby, 206
Blister-pearl, 296
Bloodstone, 247
Blue felspar, 255
Blue ground, 143, 147
Blue John, 285
Boart, 103, 129, 133
Bohemian garnet (pyrope), 207, 212
Bone turquoise, 259
Boodt, A. B. de, 132, 213
Borgis, Hortensio, 161
Borneo stones, 154, 170
Bort, _v._ Boart, 103, 129, 133
Bottle-stone, 284
Boule, 118
Bowenite, 263
Braganza diamond, 170
Brazil stones, 138, 165, 166, 169, 194 _et seq._, 201, 215, 223,
236, 243, 244, 248, 266, 269, 270, 274
Brazilian emerald, 111, 220, 221
peridot, 221
sapphire, 111, 221
topaz, 111, 197
Brilliant form of cutting, 92
Brilliant, Scientific, 122
Bristol diamonds, 243
Bruting, 100
Burma stones, 178, 205, 223, 227, 263
Button-pearl, 295
Byes, Bywaters, 136, 150
Cabochon form of cutting, 88
Cacholong, 251
Cairngorm, 239
Callaica, callaina, callais, 258
Calcite, 40, 289
California stones, 156, 195, 202, 224, 259, 265, 267, 275
Californite, 264, 275
Cape-ruby, 213
Carat weight, 72, 84
Carbon, 129
Carbonado, 129
Carborundum, 105
Carbuncle, 89, 215
Carnelian, 247
Cascalho, 139
Cassiterite, 281
Cat’s-eye (chrysoberyl), 38, 90, 233
(quartz), 39, 90, 240
(tourmaline), 39, 219
Hungarian, 244
Ceylon stones, 181, 195, 201, 205, 212, 215, 216, 223, 232, 236,
237, 243, 244, 255, 267, 274, 279, 284
Ceylonese peridot (tourmaline), 221
Ceylonite, 204
Chalcedony, 246
Chatoyancy, 38
Chert, 247
Chessylite, 287
Chrysoberyl, 233
Chrysocolla, 288
Chrysolite (chrysoberyl), 233
(peridot), 225
Chrysoprase, 247
Church, Sir Arthur, 61, 211, 231
Cinnamon-stone, 211
Citrine, 239
Cleavage, 80, 100, 149
Close goods, 149
Colenso diamond, 131
Colour, 53
Colour dispersion, 20, 97
Conchiolin, 293
Coral, 298
Cordierite, 266
Cornish diamonds, 243
Corundum, 172
Crocidolite, 39, 240
Crookes, Sir William, 132, 153
Cross facet, 93
Crystal, 6, 7, 8
Rock-, 97
Cubic system, 8
Culet facet, 93
Cullinan diamond, 94, 100, 168
Culture pearls, 297
Cumberland diamond, 164
Cyanite (Kyanite), 79, 273
Cymophane, 234
Darya-i-nor diamond, 162
De Beers diamonds, 167
Demantoid, 216
Density, 63
Deviation, Minimum, 30
Diamond, Characters of, 128
cutting, 90
gauges, 86
Glaziers’, 135
mining, 146
Occurrence of, in—
Borneo, 154
Brazil, 139
German South-West Africa, 155
India, 138
New South Wales, 154
Rhodesia, 155
South Africa, 139
Origin of, 151
-point, 91
-rose, 92
-table, 91
Diamonds, Classification of, 136, 149
Historical, 157
Prices of, 135
Dichroism, 55
Dichroite, 266
Dichroscope, 55
Diffusion column, 65
Diopside, 272
Dioptase, 280
Dispersion, Colour, 20, 24, 97
Disthene, 273
Dop, 102
Double refraction, 28, 40
Doublet, 125
Dresden diamond, 171
Drop-stone, 94
Duke of Devonshire’s emerald, 191
Edwardes ruby, 175
Electrical characters, 82
Emerald, 89, 184
Brazilian, 220, 221
Evening, 225
Oriental, 111, 172
Scientific, 122
Uralian, 216
Emeraldine, 247
Emery, 175
English Dresden diamond, 166
Enstatite, 271
Epidote, 275
Essence d’Orient, 126
Essonite (Hessonite), 211
Euclase, 269
Eugénie diamond, 164
Evening emerald, 225
Excelsior diamond, 167
Extinction, 45
Faceting machine, 105
False topaz, 239
Felspar, 254
Fire, 20, 96
Fire-marble, 289
Fire-opal, 251
Flats, 150
Flêches d’amour, 240
Flint, 247
Floors, 147
Fluor, 285
Frémy, E., 115
Garnet, 207
Green, 271
Gaudin, M. A. A., 115
Gauges, Diamond, 86
Girdle, 92
Glass, 7, 124
Gnaga Boh ruby, 180
Goniometer, 30
Grain, Pearl, 86
Graphite, 129
Greaser, 149
Great Mogul diamond, 161
Great Southern Cross group of pearls, 294
Great Table diamond, 162
Great White diamond, 167
Green garnet, 271
Greenstone, 261
Grossular, 211
Habit, 12
Hardness, 78
Haüynite, 286
Heavy liquids, 64
Hematite, 282
Hessonite, 211
Hexagonal system, 10
Hiddenite, 266
Hope cat’s-eye, 237
chrysolite, 237
diamond, 170
pearl, 294
sapphire, 121
Hornstone, 247
Hungarian cat’s-eye, 244
Hyacinth, 211, 228
Hydrophane, 250
Hydrostatic weighing, 72
Hypersthene, 271
Iceland-spar, 40, 44
Idocrase, 274
Imitation stones, 124
Imperial diamond, 167
Index of refraction, 16
India stones, 137, 181, 194, 215, 243, 244, 248, 290
Indicators, 65
Indicolite, 221
Interference of light, 39, 48
Iolite, 266
Iris, 240
Isle of Wight diamonds, 243
Isomorphous replacement, 13, 19
Jacinth, 211, 228
Jade, 260
Jadeite, 262
Jargoon, 228
Jasper, 247
Jehan Ghir Shah diamond, 163
Jigger, 149
Jubilee diamond, 167
Kauri-gum, 299
Khiraj-i-Alam ruby, 206
Kimberlite, 152
King topaz, 181, 201
Klein’s solution, 67
Koh-i-nor diamond, 137, 158
Kunz, Dr. G. F., 186, 224, 262, 265
Kunzite, 265
Kyanite, 79, 273
Labradorite, 255
La Pellegrina pearl, 294
Lapis lazuli, 286
Lazurite, 286
Lozenge facet, 93
Lumachelle, 289
Lustre, 37
Maacles, Macles, 12, 150
Madagascar stones, 195, 224, 243, 265, 266
Malachite, 287
Malacolite, 272
Manufactured stones, 113
Marble, 289
Mattan diamond, 155, 170
Matura diamonds, 232
Mazarin, Cardinal, 92
Meerschaum, 288
Mêlée, 136
Methylene iodide, 26, 66
Metric carat, 85, 87
Milky-quartz, 240
Minimum deviation, 30
Mocha-stone, 247
Moe’s gauge, 87
Mohs’s scale of hardness, 78
Moissan, Henri, 153
Moldavite, 283
Monoclinic system, 11
Moon of the Mountains diamond, 162
Moonstone, 39, 255
Morganite, 186, 195
Moroxite, 279
Moss-agate, 247
Mother-of-emerald, 240
Mother-o’-pearl, 292
Nacre, 292
Napoleon diamond, 164
Nassak diamond, 163
Negative double refraction, 45
Nephrite, 261
Nicol’s prism, 44
Nizam diamond, 162
Obsidian, 283
Occidental topaz, 111, 239
Odontolite, 259
Off-coloured diamonds, 130
Olivine (demantoid), 216
(peridot), 225
Onyx, 247
Opal, 39, 249
Fire, 251
-matrix, 251
Opalescence, 39
Optical anomalies, 47
Optic axes, 49
Oriental almandine, 112, 172
amethyst, 111, 172
emerald, 111, 172
topaz, 111, 172
Orient of pearls, 292
Orloff diamond, 160
Orthoclase, 254
Orthorhombic system, 11
Pacha of Egypt diamond, 165
Paste, 47, 124
Paul I diamond, 171
Pavilion, 93
Pavilion facet, 93
Pear-drop pearls, 292
Pear-eye pearls, 292
Pearl, 291
grain, 86
imitations, 126
Pendeloque, 94
Peridot, 225
Brazilian, 221
Ceylonese, 221
Peruzzi, Vincenzio, 92
Phenakite, 269
Pigott diamond, 164
Pipes, 152
Pistacite, 275
Pitt diamond, 100, 159
Plasma, 247, 264
Pleochroism, 57
Pleonaste, 204
Pliny, 6, 88, 138, 184, 191, 241, 249
Polar Star diamond, 163
Polarization, 42
Porter-Rhodes diamond, 166
Positive double refraction, 45
Prase, 240, 247
Prehnite, 278
Pycnometer, 75
Pyrites, 282
Pyrope, 212
Quartz, 50, 238
Quoin facet, 93
Rainbow-quartz, 240
Reconstructed stones, 116
Reef, 144
Reflection of light, 14
Refraction of light, 15
Refractive index, 16
Refractometer, 22, 50
Regent diamond, 100, 159
Retgers’s salt, 69
Rhodes, Cecil J., 145
Rhodesia stones, 155, 183, 213, 236
Rhodolite, 62, 214
Rhodonite, 287
Rock-crystal, 97, 239
Rock-drill, 134
Röntgen rays, 83
Rose form of cutting, 91
Rose-quartz, 240
Rospoli sapphire, 182
Rotation of plane of polarization, 50
Rubellite, 220, 223
Rubicelle, 203
Ruby, 98, 110, 172
Balas-, 203
Cape-, 213
Sancy diamond, 161
Sapphire, 98, 110, 172
Brazilian (tourmaline), 221
-quartz, 244
Water- (iolite), 266
Water- (topaz), 201
Sard, 247
Sardonyx, 247
Saussurite, 263
Schorl, 221
Scientific alexandrite, 122
brilliant, 122
emerald, 122
topaz, 121
Scotch topaz, 239
Seed pearls, 294
Serpentine, 289
Setting of gem-stones, 107
Shah diamond, 163
Sheen, 39
Shepherd’s Stone diamond, 163
Siam stones, 180
Siberia and Asiatic Russia stones, 182, 188, 194, 201, 217, 223,
236, 244, 256, 262, 269, 270, 287
Siberite, 221
Siderite, 244
Silver-thallium nitrate, 69
Skew facet, 93
Skill facet, 93
Smoky quartz, 240
Snell’s laws, 16
Soapstone, 288
Sodalite, 286, 287
Sonstadt’s solution, 67
South Africa stones, 139 _et seq._, 166, 167 _et seq._, 213,
232, 244, 264, 271
Spanish topaz, 239
Specific gravity, 63
Specific-gravity bottle, 75
Spectroscope, 59
Spectrum, 20, 25
Spectrum, Absorption, 59
Spessartite, 216
Sphene, 276
Spinel, 203
Spodumene, 265
Spotted stones, 149
Star-facet, 92
Star of Africa diamond, 168
Star of Este diamond, 165
Star of Minas diamond, 169
Star of South Africa diamond, 141, 166
Star of the South diamond, 139, 165
Starstones, 38, 177
Steatite, 288
Step form of cutting, 98
Stewart diamond, 166
Strass, 124
Sunstone, 255
Synthetical stones, 113
Syriam, Syrian, garnet, 215
Table facet, 92
Table form of cutting, 91
Tavernier, J. B., 91, 129, 137, 161, 162, 170
Templet facet, 92
Tetragonal system, 9
Thulite, 289
Tiffany diamond, 171
Tiger’s-eye, 39, 240
Timur ruby, 206
Titanite, 276
Topaz, 197
Brazilian, 197
False, 239
Occidental, 111, 239
Oriental, 111, 173
Scientific, 121
Scotch, 239
Spanish, 239
Topazolite, 216
Total-reflection, 18, 21
Tourmaline, 43, 219
Trap form of cutting, 98
Trichroism, 57
Triclinic system, 12
Triplet, 126
Turquoise, 257
Turquoise-matrix, 258
Tuscany diamond, 165
Twinning, 12, 47
Uniaxial double refraction, 45, 48 57
Uralian emerald, 217
Uvarovite, 218
Variscite, 259
Verdite, 264
Verneuil, A. V. L., 116
Vesuvianite, 274
Victoria diamond, 167
Violane, 287
Wart-pearl, 296
Water (of diamonds), 129
(of pearls), 292
Water-chrysolite, 284
-sapphire (iolite), 266
-sapphire (topaz), 201
White opal, 249
White Saxon diamond, 165
Wollaston, W. H., 133
X-rays, 83
Yellow ground, 143
Zircon, 228
_Printed by_ MORRISON & GIBB LIMITED, _Edinburgh_
+--------------------------------------------------------------------+
| FOOTNOTES: |
| |
| [1] The word medium is employed by physicists to express any |
| substance through which light passes, and includes solids such as |
| glass, liquids such as water, and gases such as air; the nature |
| of the substance is not postulated. |
| |
| [2] Methylene iodide must be heated almost to boiling-point to |
| enable it to absorb sufficient sulphur; but caution must be |
| exercised in the operation to prevent the liquid boiling over |
| and catching fire, the resulting fumes being far from pleasant. |
| It is advisable to verify by actual observation that the liquid |
| is refractive enough not to show any shadow-edge in the field of |
| view of the refractometer. |
| |
| [3] γωνία, angle; μέτρον, measure. For details of the |
| construction, adjustment, and use of this instrument the reader |
| should refer to textbooks of mineralogy or crystallography. |
| |
| [4] A cleavage flake of topaz may conveniently be used to show |
| the phenomenon, but owing to the great width of the angle the |
| “eyes” are invisible. |
| |
| [5] In accordance with the usual custom the angle between the |
| facets is taken as that between their normals, or the supplement |
| of the salient angle. |
| |
| [6] The word paste is derived from the Italian, _pasta_, food, |
| being suggested by the soft plastic nature of the material used |
| to imitate gems. |
| |
| [7] Cf. below, p. 149. |
| |
| [8] The least and the greatest of the refractive indices of |
| doubly refractive species are given. |
| |
| [9] The dispersion is the difference of the refractive indices |
| corresponding to the B and G lines of the solar spectrum. The |
| value for crown-glass is ·016. |
| |
+--------------------------------------------------------------------+
INTERESTING AND IMPORTANT BOOKS
JEWELLERY. By CYRIL DAVENPORT, F.S.A. With a Frontispiece in Colour
and 41 other Illustrations. Second Edition. Demy 16mo.
[_Little Books on Art._
JEWELLERY. By H. CLIFFORD SMITH, M.A. With 50 Plates in Collotype,
4 in Colour, and 33 Illustrations in the text. Second Edition.
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GOLDSMITHS’ AND SILVERSMITHS’ WORK. By NELSON DAWSON. With 51
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numerous Illustrations in the text. Second Edition. Wide royal
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EUROPEAN ENAMELS. By H. H. CUNYNGHAME, C.B. With 58 Illustrations
in Collotype and Half-tone and 4 Plates in Colour. Wide royal
8vo, gilt top. [_Connoisseur’s Library._
ENAMELS. By Mrs. NELSON DAWSON. With 33 Illustrations. Second
Edition. Demy 16mo. [_Little Books on Art._
Transcriber’s Notes:
- Text enclosed by underscores is in italics (_italics_).
- Redundant title page has been removed.
- Blank pages have been removed.
- Front publication list moved to the back.
- Silently corrected typographical errors.
- Where possible Unicode fractions have been used, otherwise they are
formatted as example “1-5/16”.