Quick answer
To identify a crystal, look past color first. Check its luster, its natural shape or the way it breaks, then test hardness with a fingernail, a steel knife and a piece of glass. A streak on unglazed porcelain and the weight in your hand settle most of the rest. Compare the results with the chart below, or upload a clear photo to a crystal identifier for a starting point.
Look past color first
Color is the first thing everyone notices and the clue that misleads most often. Quartz can be clear, purple, yellow, pink, brown or nearly black. A green stone could be aventurine, malachite, fluorite, jade or dyed glass. Note the color, then move on to the clues below.
Work in daylight and look at a dry stone. Water, oil and polish all deepen color and hide the surface texture you need to see.
The five clues that identify most crystals
- Luster: how the surface reflects light. Glassy (quartz), metallic (pyrite, hematite), silky (selenite, tiger's eye), pearly or dull.
- Shape: six-sided points suggest quartz, cubes suggest pyrite or fluorite, and smooth rounded bubbles suggest malachite or chalcedony.
- Hardness: what scratches the stone and what it scratches, measured on the Mohs scale from 1 (talc) to 10 (diamond).
- Streak: the color of the powder left when you rub the stone on unglazed porcelain. Hematite leaves red-brown, pyrite greenish black.
- Weight: some minerals feel far heavier than they look. Pyrite and hematite weigh roughly twice as much as quartz of the same size.
Crystal identification chart
Use this chart once you have checked luster, hardness and shape. Hardness values are standard reference ranges.
| Crystal | Common colors | Mohs hardness | Luster | Best clue |
|---|---|---|---|---|
| Clear quartz | Colorless, white | 7 | Glassy | Six-sided points, scratches glass |
| Amethyst | Purple, violet | 7 | Glassy | Uneven color zones, darker at the tips |
| Citrine | Pale yellow to smoky gold | 7 | Glassy | Natural citrine is pale; burnt orange with a white base is usually heated amethyst |
| Rose quartz | Pale pink | 7 | Glassy to greasy | Cloudy pink chunks, almost never in points |
| Smoky quartz | Brown to grey-black | 7 | Glassy | Transparent brown with a quartz shape |
| Calcite | White, honey, orange, blue, green | 3 | Glassy to pearly | A steel knife scratches it; fizzes in dilute acid |
| Fluorite | Purple, green, blue, banded | 4 | Glassy | Cubes or octahedra, color bands, a knife scratches it |
| Selenite (gypsum) | Colorless to white | 2 | Silky to pearly | A fingernail scratches it |
| Labradorite | Grey with blue or gold flash | 6 to 6.5 | Glassy | Flash of color at certain angles |
| Obsidian | Black, sometimes with a sheen | 5 to 5.5 | Glassy | Natural glass with curved, shell-like breaks |
| Pyrite | Brassy gold | 6 to 6.5 | Metallic | Cubic crystals, heavy, greenish-black streak |
| Hematite | Steel grey to black | 5.5 to 6.5 | Metallic | Heavy, red-brown streak |
| Malachite | Bright green, banded | 3.5 to 4 | Silky to dull | Light and dark green rings |
| Tiger's eye | Golden brown | About 7 | Silky | A band of light that moves as you tilt it |
| Amazonite | Blue-green | 6 to 6.5 | Glassy | White streaks and grid-like patterns |
How to do a scratch test safely
Hardness is the most useful test you can do at home. Always test a small, hidden spot, and never test a polished stone you plan to sell.
- Fingernail (about 2.5): scratches selenite and other gypsum.
- Copper coin (about 3.5): scratches calcite.
- Steel knife or nail (about 5.5): scratches fluorite, calcite and malachite, but not quartz.
- Glass (about 5.5): quartz, agate, jasper and tiger's eye scratch it. Glass, obsidian and softer stones do not.
Do a streak test
Rub a corner of the stone across the back of an unglazed bathroom tile. Many minerals leave a powder whose color differs from the stone. Hematite looks silver but streaks red-brown. Pyrite looks gold but streaks greenish black. Quartz and other hard stones are harder than the tile and leave no streak, which is a clue in itself.
Check the weight in your hand
Specific gravity measures how heavy a mineral is compared with water. Quartz is about 2.65, so most quartz family stones feel ordinary. Pyrite is about 5 and hematite about 5.3, so they feel surprisingly heavy. Resin and plastic fakes feel too light.
Take a photo an identifier can read
A clear photo is enough to name most common crystals and to narrow the rest to a few candidates. The free crystal identifier uses the same clues as this guide: color, luster, shape and patterns.
- Use daylight near a window and turn off filters.
- Put the stone on a plain white or grey background and let it fill the frame.
- Photograph a natural face, a point or a broken edge if the stone has one.
- Keep the stone dry and wipe off dust.
- Add notes about anything the photo cannot show, such as weight or what scratched it.
When to stop guessing
Home tests cannot detect lab-grown stones, many treatments or the difference between some gem species. If a stone is expensive, sentimental or about to be sold, ask a gemologist for a refractive index reading or send it to a gem lab.
Frequently asked questions
What is the easiest way to identify a crystal?
Start with a clear photo in daylight and an online crystal identifier to get two or three candidates. Then use a scratch test, a streak test and the weight in your hand to decide between them.
Can you identify a crystal by color alone?
Rarely. Quartz alone comes in clear, purple, yellow, pink, brown and black, and many different minerals share the same green or blue. Treat color as a hint and confirm with hardness, luster and shape.
How do I tell quartz from glass?
Quartz has a hardness of 7 and scratches ordinary glass, while glass will not scratch quartz. Glass often shows round gas bubbles or swirl lines under a magnifier and warms up in your hand faster than quartz.
Is a photo identification reliable?
For common crystals with a distinctive color, shape or pattern, a good photo is usually enough. White, clear and grey stones are harder, and a photo cannot detect lab-grown or treated stones. Use the result as a starting point and confirm valuable stones with a gemologist.
Sources and further reading
The references we used to prepare this guide.
