Idocrase 6-1/2 Garnets (see also "Red Garnets" below) 6-1/2-7-1/2 Axinite 6-3/4 Jadeite 6-3/4 Quartz, including Rock-crystal, Amethyst, Jasper, Chrysoprase Citrine, etc. 7 Jade 7 Dichorite (water sapphire) 7-7-1/2 Cordierite 7-1/4 Red Garnets (see also Garnets above) 7-1/4 Tourmaline 7-1/4 Andalusite 7-1/2 Euclase 7-1/2 Staurolite 7-1/2 Zircon 7-1/2 Emerald, Aquamarine, or Beryl 7-3/4 Phenakite 7-3/4 Spinel 8 Topaz 8 Chrysoberyl 8-1/2 The Corundum group embracing the Ruby, Sapphire, etc. 9 Diamond 10 (See also list of stones, arranged in their respective colours, in Chapter XII.) The method of testing is very simple. A representative selection of the above stones, each with a sharp edge, is kept for the purpose of scratching and being scratched, and those usually set apart for tests in the various groups, are as follows:-- 1 Talc 2 Rock-salt, or Gypsum 3 Calcite 4 Fluorspar 5 Apatite 6 Felspar 7 Quartz 8 Topaz 9 Corundum 10 Diamond The stone under examination may perhaps first be somewhat roughly classified by its colour, cleavage, and general shape. One of these standard stones is then gently rubbed across its surface and then others of increasingly higher degrees, till no scratch is evident under a magnifying glass. Thus if quartz ceases to scratch it, but a topaz will do so, the degree of hardness must lie between 7 and 8. Then we reverse the process: the stone is passed over the standard, and if both quartz and topaz are scratched, then the stone is at least equal in hardness to the topaz, and its classification becomes an easy matter.