Approximate average of
(1) hardness
(2) specific gravity (4) Dispersion
(3) refractive index (5) Durability
Species (1) (2) (3) (4) (5) Usual color range
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