Smoky Quartz
Last updated: April 2026
The brown to black variety of quartz, colored by natural irradiation of aluminum impurities.
Smoky Quartz has a specific gravity of 2.65 and a refractive index of 1.544–1.553, with a Mohs hardness of 7. It is uniaxial +.
Physical & Optical Properties
RI Range1.544–1.553
SG Range2.63–2.65
SG Typical2.65
Hardness (Mohs)7
Crystal SystemTrigonal
Optic CharacterDR Uniaxial (+)
Birefringence0.009
Dispersion0.013
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismWeak
ColorsBrown, Black
SpeciesQuartz
Related: Quartz Varieties
Key Differentiators
- 'Bull's eye' optic figure
- Color caused by natural irradiation
- RI and SG specific to quartz
Treatments
- Irradiation (to create or deepen color)
Price Context
Natural — low ($/ct)$2
Natural — high ($/ct)$10
NotePer carat; dark brown to black (Morion variety); large clean stones are common
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying a smoky quartz? GemID walks through these tests in order — RI, SG, fluorescence, and more.
Try GemID Free →Studying for the GIA, FGA, or FEEG practical? Smoky Quartz is one of the 130 species in GemID’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →