COMPARE GUIDE
Brown GlassVSSmoky Quartz
Side-by-side comparison of physical properties, fluorescence, and crystal system — to identify by observation.
- ◎ is higher in Smoky Quartz, giving a numerical distinguishing point.
Note: properties whose numeric ranges do not overlap are auto-extracted. Both are measurable with a refractometer or heavy-liquid bath.
| Property | A: Brown Glass | B: Smoky Quartz | Verdict |
|---|---|---|---|
| Refractive index (RI) | 1.480–1.700 | 1.544–1.553 | Overlap |
| Specific gravity (SG) | 2.30–4.50 | 2.64–2.66 | Overlap |
| Mohs hardness | 5.0–6.0 | 7.0 | B higher |
| Birefringence | — | 0.009 | — |
| Dispersion | — | — | — |
| Property | A: Brown Glass | B: Smoky Quartz |
|---|---|---|
| Crystal system | 非晶質 | 三方晶系 |
| Pleochroism | — | 弱〜中（茶・赤茶） |
| Chelsea filter | — | inert |
| UV (long-wave) | — | inert |
| UV (short-wave) | weak (yellow) | inert |
◆Smoky quartz (SiO₂, Mohs 7, SG 2.65, RI 1.544–1.553, doubly refractive, 0.013) is the natural species that brown glass most often imitates. Refractometer reads 1.544–1.553 for smoky quartz versus 1.50–1.70 for glass (significant overlap, so this test alone is non-diagnostic). The decisive separation comes from polariscope examination (smoky quartz doubly refractive, glass singly refractive) and from nclusions, color zoning, and 'phantom' growth surfaces; glass shows regular round gas bubbles and pressing-die seams). Mohs 7 smoky quartz is unaffected by a steel-knife scratch test that easily marks Mohs 5–6 glass. The natural irradiation that produces smoky-quartz color in nature can be reproduced with cobalt-60 gamma-ray treatment on colorless rock crystal, producing irradiated smoky quartz that is gemologically natural quartz with disclosed treatment — distinct from glass imitations. Disclosure as 'glass' is required under FTC Jewelry Guides §23.25.
Distinguishing tools
Tools that decide between Brown Glass and Smoky Quartz in practice.
Note: this page is auto-generated from published GIA / CGL reference values. Individual stones, treatments, and synthetics may fall outside these ranges. For a definitive identification, consult an accredited gem laboratory.