hardness, 39-41
specific gravity, 48-50

Lustre, 26, 28

Lustreless, definition of, 29

Lynx-eye stones, 87

Magnesia-alumina garnets, 102, 103
carbuncle, or anthrax, 102
noble, 103
pyrope, 102

Magnetic and electric influences, 57-61

Malachite, 11

Manganese-alumina garnets, 103
spessartine, or spessartite, 103

Masculine stones, 85

Melanite, 101

Menilite (opal), 36

Metallic-lustre stones, 28, 29

Mohs's table of hardness, 39-41

Noble garnet, 103
or precious opal, 35

Non-diaphanous stones, 28

Odontolite, 106

Olivine corundum (see "Chrysolite"), 85

Opal, 11
varieties of, 35, 36

Opalescence (not to be confused with "Change of Colour" and "Play of Colour,"
which see; see also "Fire"), 36, 37

Oriental amethyst, 85
cat's eye (see "Cat's eye")
emerald, 85
garnet, 101
topaz, 85

Origin of precious stones, 7

Paste, or strass, for imitation stones, composition of, 71

Pavilion portion of cut stones, 66

Pearly-lustre stones, 28, 29

Peridot (see "Noble Chrysolite"), 85

Pink-coloured stones, list of (see also Red), 77

Pinked topaz, 92

Phosphorescence, 26, 30

Physical properties:--
A.--Crystalline structure, 13
B.--Cleavage, 19
C.--Light, 26
D.--Colour, 32
E.--Hardness, 39
F.--Specific gravity, 45
G.--Heat, 52
H.--Magnetic and electric influences, 57

Play of colour (not to be confused with "Change of Colour" and "Opalescence,"
which see; see also "Fire"), 36, 37

Pleochroism, 33

Polarisation, electric, 58, 59
of light, 26, 27

Polariscope, 27, 28

Polishing precious stones, 3, 4

Polymorphism in precious stones, 25

Precious, or noble opal, 35

Pseudomorphism in precious stones, 23, 24

Pyreneite, 101

Pyro-electricity, development and behaviour of, 58-60

Pyrope, 102

Qualities of precious stones, 1, 3

Red and rose-coloured stones, list of (see also Pink), 76, 77

Reflection of light, 26, 28

Refraction of heat, 52-55
light, 26, 27

Reproduction of crystalline form, 20, 21

Resinous lustre stones, 28, 29

Rock-crystal, 11

Romanzovite, 102

Rose-coloured stones (see Red, above), 76, 77

Rose, or rosette-cut stones, 65

Rothschild's testing solution, 73

Ruby, characteristics of, 83
composition of, 10

Sapphire, amethyst, 85
and its varieties, 84, 85
cleared, 86
diamonds, 87
indigo, 86
ink, 85
the blue, composition of, 10, 85
water, 86

Semi-