COMPARE GUIDE
Clear GlassVSRock Crystal / Quartz
Side-by-side comparison of physical properties, fluorescence, and crystal system — to identify by observation.
- ◎ is higher in Rock Crystal / 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: Clear Glass | B: Rock Crystal / 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: Clear Glass | B: Rock Crystal / Quartz |
|---|---|---|
| Crystal system | 非晶質 | 三方晶系 |
| Pleochroism | — | — |
| Chelsea filter | inert | inert |
| UV (long-wave) | inert | inert |
| UV (short-wave) | inert | inert |
◆Rock crystal (colorless quartz, SiO₂, Mohs 7, SG 2.65, RI 1.544–1.553, doubly refractive, 0.013) is the natural species that clear glass most often imitates. Refractometer reads 1.544–1.553 for rock crystal versus 1.50–1.70 for glass (overlap requires combined testing). The decisive separation comes from polariscope examination (rock crystal 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 rock crystal is unaffected by a steel-knife scratch test that easily marks Mohs 5–6 glass. Rock crystal is generally cooler to touch than glass owing to higher thermal conductivity. Disclosure as 'glass' or 'crystal' (per EU Directive 69/493/EEC for the latter) is required.
Distinguishing tools
Tools that decide between Clear Glass and Rock Crystal / 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.