The hardness of diopside is 5 to 6; specific gravity, 2.9 to 3.5; lustre, vitreous to greasy. It is transparent to translucent, brittle, cannot be dissolved by acids, and melts before the blow-pipe. It is composed of: Silica 54 Lime 24 Magnesia 18 Ferrous oxide 4 This mineral is grayish-white to pearl-gray, and greenish-white to greenish-gray. The best green transparent specimens are from the Mussa Alp and Zillerthal, but it is also found in the Urals and the United States. FLUOR SPAR. This mineral occurs in many colors, often approaching the finer gems in appearance, and bearing the commercial names of false ruby, false emerald, false topaz, etc., etc., according to its color. Fluor spar is brittle, 4 in hardness, has the specific gravity of 3.1 to 3.2, single refraction, is transparent to translucent, has a vitreous lustre, phosphoresces when heated, is attacked by acids, and melts before the blow-pipe. It is composed of: Fluorine 48.7 Calcium 51.3 White, yellow, green, rose- and crimson-red, violet-blue, sky-blue, and brown, wine-yellow, greenish-blue, and gray are the colors of this many-tinted mineral. Fluor spar is found in England, Norway, Baden, Nova Scotia, Thuringia, the Alps, Saxony, and the United States. Large pieces of this mineral are made into beautiful vases and ornaments. HYPERSTHENE. Handsome specimens of hypersthene or Labrador hornblende are used for ornamental purposes. This mineral is found in crystalline masses, has the hardness of 6, specific gravity 3.3 to 3.4, lustre pearly to metallic. It is translucent to opaque, brittle, and fuses before the blow-pipe. It consists of: Silica 54.2 Magnesia 24.1 Protoxide of iron 21.7 Hypersthene occurs in dark-brown, green, grayish-black, greenish-black, and jet-black colors, and is found in the isle of Skye, the Hartz Mountains, Saxony, Labrador, Greenland, Norway, Sweden, Bohemia, Thuringia, and the United States. QUARTZ. The quartz group is the largest and most diversified among precious stones. Quartz occurs _massive_, in concretions, and in confused crystalline masses. On account of the abundance of the massive kinds, such as jasper, agates, onyx, etc., some writers place the quartz group under the head of semi-precious stones, and lately the United States customs authorities have gone further in that direction, and have ruled that “because of the abundance and comparative cheapness of agates, onyxes, etc., they were no longer precious stones.” This position, however, the custom-house speedily abandoned, and, for dutiable purposes at least, the quartz family, in all its ramifications, is recognized as belonging to the precious stones.