Beryl 7¾ 2.70 1.58 Low High Green (emerald), blue-green (aquamarine), pink (morganite), colorless (goshenite) Chrysoberyl 8½ 3.71 1.75 Low High Yellow, green, brown Corundum 9 4.00 1.77 Low High Red (ruby), various (sapphire) Diamond 10 3.52 2.42 High High Colorless Garnet group 7½ 3.70- 1.74- Medium High Yellow, red, green, brown 4.16 1.89 to high Jade 6½ 2.96 1.62 None High Green, white (nephrite) Jade 7 3.33 1.66 None High Green, white (jadeite) Opal 6 2.10 1.45 None Low Red, dark gray, orange, white, with or without varicolored fire Pearl 3½ 2.71 None None Low White Peridot 6½ 3.34 1.68 Low Medium Yellow-green, brownish green Quartz 7 2.65 1.55 Low High Purple (amethyst), yellow (citrine), colorless (rock crystal) Spinel 8 3.60 1.72 Low High Shades of red, green, blue, violet Spodumene 7 3.18 1.66 Low Low Colorless, pink, yellow, green Topaz 8 3.54 1.63 Low Medium Colorless, sherry, pink, blue Tourmaline 7 3.06 1.63 Low High Wide range, except bright red Zircon 7 4.02 1.81 High High Almost colorless, blue, brown, green, yellow GEMSTONES FOR THE COLLECTOR A number of mineral species have produced cut gemstones that fulfill every necessary requirement of beauty, durability, and rarity, but their popularity and commercial success have been sharply limited because of insufficient supply. In some cases of even adequate supply such gemstones do not compete with other, more plentiful kinds that exhibit the same characteristics. The scarcity of these minerals does not diminish their standing as potential gem material—it merely points up the effect of accidental natural distribution of these species. [Illustration: A magnificent set of 16 matched sphenes from Switzerland, gift of Nina Lea, almost encircles a 110-carat sinhalite (a rare magnesium borate) and a 22-carat kornerupine, both from Ceylon. The man’s gold ring indicates the sizes of these unusual stones.]