The color of a mineral or gemstone is one of the primary attributes used for identification, but it is, unfortunately, one of the least diagnostic and useful (except in a handful of cases). The colors reported include all those mentioned in the mineralogical or gemological literature. These are useful to gemologists primarily as a guide as to what could be expected in the future; that is, the potential color of a gemstone. A mineral may, at any time, be found in gem quality in a new or unfamiliar color. A good example is zoisite, which is found in Africa in a striking blue variety in the 1960s and given the trade name tanzanite.

The streak (color of a mineral powder) is listed where it is useful for identification. This characteristic applies almost exclusively to opaque, metallic minerals because the powder of most transparent minerals is colorless (white).

The color names applied to gems and minerals have become familiar through long usage. Some gem color names, such as “pigeon’s-blood” (ruby) or “padparadschah” (sapphire) are vague, but have remained in the marketplace because no useful alternatives existed. However, accurate color measurement instrumentation is now available and is about to revolutionize the gemstone…