Identifying a crystal correctly matters for more than curiosity. Mislabeled stones are common in the retail trade, heat-treatment and dyeing are widespread, and glass imitations are sold as "quartz points" often enough that a five-minute check is worth the habit. The tests below are the same ones used informally by mineral collectors before a specimen ever reaches a lab, based on standard mineralogical properties described in reference works such as the Mohs scale of mineral hardness.
The core identification tests
Hardness (Mohs scale): scratch the specimen with a reference material — a fingernail (2.5), a copper coin (3.5), a steel knife blade (5.5), or a purpose-bought hardness pick set. Quartz sits at 7; if a steel blade scratches your "quartz," it likely isn't.
Streak test: drag the specimen across an unglazed porcelain streak plate. The powder left behind is often a more reliable colour indicator than the stone's surface — hematite streaks reddish-brown even when the specimen looks black and metallic.
Luster: describe how the surface reflects light — vitreous (glassy, like quartz), resinous, pearly (like selenite), metallic, or dull/earthy. Luster alone rules out many mismatches.
Cleavage and fracture: note whether the stone breaks along flat, predictable planes (cleavage, as with selenite and mica) or in curved, shell-like fractures (conchoidal fracture, typical of quartz and obsidian).
Specific gravity: weigh the stone dry, then submerged in water, and compare the ratio. Denser stones like hematite (SG ~5.2) separate easily from lighter look-alikes.
Comparison: six common crystals
| Mineral | Mohs Hardness | Luster | Typical Formation | Common Source Regions |
|---|---|---|---|---|
| Quartz | 7 | Vitreous | Igneous & hydrothermal veins | Brazil, Madagascar, USA |
| Amethyst | 7 | Vitreous | Volcanic geodes | Brazil, Uruguay, Zambia |
| Citrine | 7 | Vitreous | Natural or heat-treated quartz | Brazil (natural rare) |
| Selenite | 2 | Pearly | Evaporite deposits | Mexico, Morocco |
| Obsidian | 5–5.5 | Vitreous | Rapidly cooled volcanic glass | Mexico, Iceland, USA |
| Black Tourmaline | 7–7.5 | Vitreous | Granite pegmatites | Brazil, Nigeria, USA |
Field kit vs. lab certification
Most hobbyists never need a lab. A basic identification kit — hardness picks, a streak plate and a jeweler's loupe — typically runs $20–$45 and answers the majority of everyday questions.
- Field kit pros: inexpensive, fast, no shipping required, teaches the underlying skill.
- Field kit cons: can't confirm trace-element treatments (like heat-treated citrine) or detect synthetic growth patterns.
- Lab certification pros: gemological labs use refractometry and spectroscopy to confirm treatments, origin and authenticity — useful for insured or high-value pieces.
- Lab certification cons: costs $50–$150 per stone depending on the lab, and turnaround can take one to three weeks.
Common misidentifications
Leaded glass is routinely sold as "quartz" — check hardness and look for tiny gas bubbles under a loupe, which real quartz never contains. Much commercial citrine is heat-treated amethyst, identifiable by a slightly smoky or orange-brown tint rather than pale lemon-yellow. "Rainbow moonstone" is frequently labdorite feldspar rather than true moonstone, distinguished by its blue-grey sheen versus moonstone's adularescence.
A simple step-by-step routine
- Examine luster and colour in natural light.
- Run the streak test if the specimen is opaque enough to leave a mark.
- Test hardness starting with a fingernail, working up to a steel blade.
- Check the break pattern on any existing chip or edge.
- Cross-reference your results against a mineral field guide or the comparison table above.
Once you can identify a stone confidently, the next useful step is usually understanding what it has historically represented — see our guide to crystal symbolism and meanings — or how to look after it once it's home, covered in crystal care and cleansing.