It is in the qualities of hardness and brilliancy that such minerals as malachite and lapis lazuli fail; owing to their comparative softness, they would not, if cut and polished, possess the sharp edges and brilliant surface of the emerald or sapphire, and would soon become dull and rounded by friction, even by the friction of ordinary dust. Again, since they are opaque, they can never flash like the sapphire or the emerald; and yet it is quite a mistake to suppose that the necessary qualities are confined to those few stones which are familiar to everyone, such as the diamond, ruby, sapphire, emerald, garnet and amethyst. There are many others, though they are not so well known. I think we may fairly assert that such minerals as tourmaline, jargoon, peridote, spinel and chrysoberyl, though their names may be familiar, are not stones which would be recognized by any but those who are in some sense experts; while other minerals, such as sphene, andalusite, axinite, idocrase and diopside, are possibly almost unknown to most people, even by reputation. Yet all these minerals possess qualities of transparency, hardness and beauty of color which render them extraordinarily interesting and attractive as precious stones. (A number of faceted stones cut from the less known minerals were thrown upon the screen by reflected light.) Take first the hardness. A few years ago the hardness of stones was a very important character in the eyes of the mineralogist; it was one of the characters by which they were invariably identified, and a distinguished German mineralogist drew up a table by means of which the hardness of minerals can be compared. Any stone is said to be harder than the minerals of this scale which it can scratch, and softer than those by which it can be scratched. In the right hand column the gem stones are arranged according to their hardness. MOHS' SCALE OF HARDNESS. 1. Talc. 2. Gypsum. 3. Calcite. 4. Fluor. 5. Apatite. / Sphene. \ Opal. 6. Feldspar. / Diopside. \ Moonstone. / Epidote. | Idocrase. | Peridote. \ Axinite. 7. Quartz. / Quartz. | Tourmaline. | Cordierite. \ Garnet. / Andalusite. | Zircon. | Emerald. \ Phenacite. 8. Topaz. / Spinel. | Topaz. \ Chrysoberyl. 9. Corundum. / Ruby. \ Sapphire. 10. Diamond. Diamond.