The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Is a Variety of||Quartz|
|Colors||Every shade of brown.|
|Fracture||Conchoidal to uneven|
|Cleavage||None or indistinct|
|Absorption Spectrum||Not diagnostic.|
|Pleochroism||Dark stones: weak brown/reddish brown. Light stones: weak, light and darker yellowish brown.|
|Optics||o = 1.544; e = 1.553 (very constant). Uniaxial (+).|
|Optic Sign||Uniaxial +|
|Typical Treatments||Heat Treatment|
|Transparency||Transparent to opaque.|
Smoky quartz is also mistaken for topaz. It comes in every shade of brown, from a light tan to nearly black. “Chocolate citrine” is a pleasant brownish/yellow color. Smoky quartz is known for its large sizes. The person who wants a really big gem, without a really big budget, often ends up with one of these.
Smoky quartz: is in the same size league as citrine, but larger stones get very dark and opaque. Smithsonian Institution (Washington, D.C): 4500 (California) and 1695 (Brazil), plus others.