us stones, 28

Dichroscope, 33
how to make a, 33
how to use a, 34

Dimorphism in precious stones, 25

Double cabochon-cut stones, 65
refraction (see "Refraction")

Doublets, 72

Electric and magnetic influences, 57
experiments with precious stones and pithball and electroscope, 57
experiments with tourmaline, 58, 59

Emerald, 10, 11, 95, 96
oriental, 85

En cabochon-cut stones, 64

Experiments to show electric polarity, 58, 59

Facets in stones, description of the, 67, 68

Feminine stones, 85

Fire in stones (see also "Change of Colour," "Opalescence," and "Play of
Colour"), 36, 37

Fire opal, 35

Flame-coloured stones, list of, 76

Flaws, 63

Formation of precious stones, 5, 8
chemical illustration of, 8, 9

Garnet, 11, 100

Garnets
(A) iron-alumina (called also almandine and precious
or oriental garnet), 101
sub-variety, common garnet, 101
(B) lime-iron, 101
sub-variety aplome, 101
melanite, 101
pyreneite, 101
topazolite, 101
(C) lime-chrome, 101, 102
sub-variety uwarowite, 101, 102
(D) lime-alumina, 102
sub-variety cinnamon stone, 102
romanzovite, 102
succinite, 102
(E) magnesia-alumina, 102, 103
sub-variety carbuncle, or anthrax, 102, 103
noble, 103
pyrope, 102
(F) manganese-alumina, 103
sub-variety spessartine, or spessartite, 103

Girdle portion of a stone, 66

Glimmering, in lustre, definition of, 29

Glinting, or glistening in lustre, definition of, 29

_Goutte de suif_-cut stones, 65

Great Mogul diamond, 64

Green stones, list of, 78

Groups of crystals (see "Crystals")

Hardness, physical properties of, 39
table of, 39, 40, 41

Heat indexes, 54
physical properties of, 52

Hollow-cabochon, 65

Hyacinth, ordinary (a form of zircon), 85, 98
oriental, 85

Hyalite (opal), 35

Hydrophane (opal), 35

Imitations and tests of precious stones, 70

Indigo sapphires, 86

Ink sapphires, 85

Iridescence, and cause of, 37, 38

Iron-alumina garnets, 101

Jacinth, oriental, 85

Jarcon, or jargoon, 98

Koh-i-nur, 64

Lapis-lazuli, 103

Light, physical properties of, 26

Lime-alumina garnets, 102
cinnamon stone, 102
romanzovite, 102
succinite, 102

Lime-chrome garnets, 101, 102
uwarowite, 101, 102

Lime-iron garnets, 101
aplome, 101
pyreneite, 101
topazolite, 101

List of stones according to colour, 75-79