_Hardness._ _Specific Gravity._ (See Chapter VII.) (See Chapter VIII.) Aquamarine 7-3/4 2.701-2.800 Chrysoberyl 8-1/2 3.689-3.752 Chrysolite 6-7 3.316-3.528 Chrysoprase (Quartz) 7 2.670 Diamond 10 3.502-3.564 Dioptase 5 3.289 Emerald and Oriental Emerald 7-3/4 2.690 Euclase 7-1/2 3.090 Garnet (see also Red Garnet) 6-1/2-7-1/2 3.400-4.500 Heliotrope (Chalcedony) 6-1/2 2.598-2.610 Hiddenite (a variety of Spodumene) 6-1/2-7 3.130-3.200 Jade 7 3.300-3.381 Jadeite 7 3.299 Malachite 3-1/2 3.710-3.996 Peridot (a variety of Chrysolite) 6-7 3.316-3.528 Plasma (a variety of Chalcedony) 6-1/2 2.598-2.610 Quartz 7 2.670 Sapphire 9 4.049-4.060 Topaz 8 3.500-3.520 Tourmaline 7-1/4 3.148 VIOLET STONES. _Hardness._ _Specific Gravity._ (See Chapter VII.) (See Chapter VIII.) Amethyst 7 2.661 Diamond 10 3.502-3.564 Quartz (Amethyst) 7 2.670 Sapphire 9 4.049-4.060 Spinel 8 3.614-3.654 Tourmaline 7-1/4 3.160 CHATOYANT STONES. These stones are easily recognisable by their play of colour. (See Chapter XIV.) BLACK STONES. _Hardness._ _Specific Gravity._ (See Chapter VII.) (See Chapter VIII.) Diamond 10 3.502-3.564 Garnet 6-1/2-7-1/2 3.400-4.500 Jet 3-1/2 1.348 Onyx (a variety of Chalcedony) 6-1/2 2.598-2.610 Quartz 7 2.670 Tourmaline (not unlike Black Resin in appearance) 7-1/4 3.024-3.300 CHAPTER XIII. VARIOUS PRECIOUS STONES. _The Diamond._