Part 3

When the images are identical in color, the specimen may be a diamond, garnet, spinel, or glass. Should a red or ruby spinel approach the ruby in color, a quick and satisfactory test can be made with the dichroiscope, as the spinel will show two images of one color, while the ruby will show one image of aurora red and one of carmine red.

The dichroiscope is inexpensive, costing but a few dollars, and is very useful for rapidly deciding the species of many stones. The following is a partial list of doubly refracting stones and their twin colors.

───────────────────────┬────────────────────────────────── NAME OF STONE. │ TWIN COLORS. ───────────────────────┼─────────────────┬──────────────── Sapphire (blue) │ Greenish straw │ Blue Ruby (red) │ Aurora red │ Carmine red Tourmaline (red) │ Salmon │ Rose pink " (brownish red) │ Umber brown │ Columbine pink " (brown) │ Orange brown │ Greenish yellow " (green) │ Pistachio green │ Bluish green " (blue) │ Greenish gray │ Indigo blue Emerald (green) │ Yellowish green │ Bluish green Topaz (sherry) │ Straw yellow │ Rose pink Peridot (pistachio) │ Brown yellow │ Sea green Aquamarine (sea green) │ Straw white │ Gray blue Beryl (pale blue) │ Sea green │ Azure blue Chrysoberyl (yellow) │ Golden brown │ Greenish yellow Iolite (lavender) │ Pale buff │ Indigo blue Amethyst (purple) │ Reddish purple │ Bluish purple ───────────────────────┴─────────────────┴────────────────

COLORS.

The following is a partial list of the colors of precious stones:

Shades of White.—Quartz, opal, chalcedony.

Shades of Gray.—Labrador, smoky topaz, chalcedony, zircon.

Black.—Obsidian, tourmaline, jet.

Shades of Blue.—Lapis-lazuli, amethyst, chalcedony, spinel, zircon, sapphire, cyanite, tourmaline, turquois, odontolite, fluor spar.

Shades of Green.—Amazon stone, turquois, prase, beryl, blood-stone, epidote, emerald, malachite, chrysoprase, chrysolite, idocrase, olivine, garnet, chrysoberyl.

Shades of Yellow.—Opal, amber, topaz, beryl, jasper.

Shades of Red.—Garnet, carnelian, chalcedony, rose quartz, corundum, tourmaline, spinel, ruby.

Shades of Brown.—Zircon, garnet, smoky topaz, axinite, jasper.

Colorless.—Diamond, sapphire, spinel, zircon, topaz, rock crystal, moonstone.

LUSTRE.

Well polished precious stones display a decided lustre, which assists in determining their species.

The following is a list of some precious stones and their lustre:

Adamantine.—Diamond, zircon.

Resinous.—Garnet.

Vitreous.—Emerald, ruby, spinel.

Waxy.—Turquois.

Pearly.—Moonstone, opal.

Silky.—Crocidolite, quartz cat’s-eye.

Metallic.—Hematite.

Greasy.—Olivine.

Some stones vary in lustre, from vitreous to pearly, etc.

STREAK.

The streak of a mineral is the color of its powder.