QuartzMohs 7
Hexagonal prismatic crystals terminated by six-sided pyramids. Vitreous luster, no cleavage. Mohs 7 — scratches glass.
Photo: Wikipedia contributors · wikipedia
Crystal Identifier
A crystal's identity is written in its faces. Termination style, internal angles, and color zoning separate quartz from calcite and amethyst from fluorite even when raw color looks identical. This identifier reads habit and termination from a single photo, then returns three ranked candidates with the variety name where the photo supports it.
- Returns varietal names: amethyst, citrine, smoky, not just 'quartz'
- Habit-aware: prismatic, rhombohedral, cubic, dodecahedral
- Lookalike crystals to rule out per match
- Mohs hardness and luster called out where diagnostic
Reviewed by RockHoundR Field Team · Field identification & geology editors · Last verified
Quick answer
Crystals are identified by habit (the shape) and color zoning. Upload a clean photo of a single specimen with terminations visible — the identifier returns three ranked matches with variety names, Mohs hardness, and a lookalike crystal to rule out.
Crystal identification is mostly about habit — the geometry a mineral takes when free to grow. Quartz forms six-sided prisms ending in pyramidal terminations. Calcite forms rhombohedrons that look like leaning cubes. Fluorite forms cubes or octahedrons. Garnet forms dodecahedrons. The habit name often gets you to the species before color, luster, or hardness enter the picture.
Color decides variety, not species. Purple quartz is amethyst. Yellow quartz is citrine. Brown-to-black quartz is smoky. Each variety is still quartz mineralogically (Mohs 7, vitreous luster, no cleavage), but collectors and buyers care about the variety, so the identifier returns the varietal name when the photo supports it.
Photos miss three useful crystal tests: cleavage (calcite breaks into rhombs, quartz doesn't break cleanly), double refraction (calcite splits a line into two when laid on text — quartz doesn't), and streak (most clear crystals streak white, but a few don't). Use the photo result as a starting point, then run these tests to confirm.
Visual identification guide for crystals
These six cover the bulk of crystal submissions. Each card shows a reference specimen and the habit cue that separates it from its closest lookalike.
AmethystMohs 7
Purple quartz — same habit as clear quartz but with iron-induced color zoning, often deepest at the tip and fading toward the base.
Photo: Wikipedia contributors · wikipedia
CalciteMohs 3
Rhombohedral crystals (lean-sided cube shape) with three perfect cleavages. Birefringent — laid on text, splits letters into two.
Photo: Wikipedia contributors · wikipedia
FluoriteMohs 4
Cubes or octahedrons, often green, purple, or blue. Four perfect cleavages. Fluoresces under UV (where the name comes from).
Photo: Wikipedia contributors · wikipedia
TourmalineMohs 7-7.5
Long striated prismatic crystals with a triangular cross-section. Common color: schorl (black). Vertical striations are diagnostic.
Photo: Wikipedia contributors · wikipedia
GarnetMohs 6.5-7.5
Dodecahedral or trapezohedral crystals — soccer-ball-like 12- or 24-sided shapes. Deep red (almandine) to green (uvarovite). Mohs 7–7.5.
Photo: Wikipedia contributors · wikipedia
Crystal property comparison
The six common crystals side by side. Cleavage is often the deciding test when the photo isn't conclusive.
| Specimen | Hardness (Mohs) | Luster | Cleavage | Habit | Field tell |
|---|---|---|---|---|---|
| Quartz | 7 | vitreous | none | prismatic crystals with pyramidal terminations, massive, granular | Six-sided prism ending in pyramid. No cleavage. |
| Amethyst | 7 | vitreous | none | prismatic crystals in geodes | Quartz habit with purple iron coloration zoning. |
| Calcite | 3 | vitreous | perfect in 3 directions | rhombohedral, prismatic, scalenohedral, massive, stalactitic | Rhombohedral cleavage in three directions, fizzes in acid. |
| Fluorite | 4 | vitreous | perfect octahedral | cubic crystals, octahedral, dodecahedral, massive | Cubic or octahedral. Octahedral cleavage. UV fluorescent. |
| Tourmaline | 7-7.5 | vitreous | none | prismatic, vertically striated crystals, columnar | Striated prism, triangular cross-section. Pyroelectric. |
| Garnet | 6.5-7.5 | vitreous | none | dodecahedral and trapezohedral crystals, massive | 12- or 24-sided shape, deep red, Mohs 7–7.5. |
Identify by crystal habit
The shape a crystal takes when it grew freely is the single strongest visual cue.
- Prismatic (hexagonal)
- Quartz family, beryl (aquamarine, emerald), apatite, tourmaline.
- Rhombohedral
- Calcite, dolomite, siderite. Looks like a leaning cube.
- Cubic
- Fluorite, halite (salt), galena, pyrite. Pyrite cubes are striated; fluorite cubes are not.
- Dodecahedral / trapezohedral
- Garnet group — 12 or 24 rhombic faces. No other common gem mineral takes this shape.
- Octahedral
- Diamond, fluorite, magnetite, spinel. Fluorite is the only soft one.
- Tabular / platy
- Mica (muscovite, biotite), barite, gypsum. Splits into sheets along a single cleavage direction.
Identify by termination
How the crystal ends — flat, pointed, doubly terminated — is often more diagnostic than the prism itself.
- Six-sided pyramidal point
- Quartz family — clear, smoky, citrine, amethyst, rose. Same six-fold symmetry across all.
- Flat / pinacoidal
- Beryl (emerald, aquamarine) — hexagonal prism ending in a flat face.
- Wedge / scalenohedral
- Calcite — the 'dogtooth' habit. Sharp pointed terminations on rhombohedral crystals.
- Doubly terminated
- Herkimer Diamond (a quartz variety) — both ends pointed, free-grown in vugs. Rare and prized.
How the crystal identifier works
- Step 1
Photograph the crystal
Show terminations and faces. A single crystal reads more clearly than a tight cluster.
- Step 2
Add where it's from (optional)
Locality (mine, region, country) helps narrow varietal names — Arkansas quartz reads differently than Brazilian.
- Step 3
Get 3 ranked matches
Variety, habit, typical hardness, and a similar-looking crystal to rule out for each match.
Take a photo that identifies well
- Show the full termination — that's where the habit reads.
- Diffuse natural light to avoid blowing out clear specimens.
- Plain dark or white background so faces are visible.
- If it's a cluster, photograph the most distinct single crystal.
What to avoid
- Strong overhead spotlights — they hide internal color zoning.
- Wet specimens unless dry color is misleading.
- Photos where only the matrix is visible.
- Through-glass shots from a display case.
How accurate is this crystal identifier?
Habit reads well from a photo. Cleavage, streak, and refractive index do not. Here's where the tool is strong and where you should verify.
Strong on
- Specimens with clear crystal terminations — quartz, calcite, fluorite, tourmaline, garnet.
- Distinguishing varietal names from raw mineral — amethyst vs clear quartz, citrine vs smoky.
- Naming the lookalike to rule out when two species share habit (calcite vs aragonite, quartz vs beryl).
Less reliable on
- Cabochons, faceted gems, and polished material — habit is lost.
- Crystal clusters where no single specimen is dominant.
- Rare collector species without strong training-data coverage (vauxite, painite, similar).
- Anything where cleavage, streak, or double refraction would decide it.
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Crystal Identifier FAQ
Will it return a variety name or just the mineral species?
When habit, color zoning, and luster support it, the identifier returns the variety — Amethyst, Citrine, Smoky Quartz — rather than the generic species. If the image is ambiguous it stays at the species level (e.g. 'Quartz') and explains which variety it could be.
How do I tell quartz from calcite from a photo?
Quartz has glassy luster and a six-sided prism ending in a six-sided pyramid; calcite shows rhombohedral cleavage (three flat faces meeting at oblique angles) and a duller pearly-to-vitreous luster. Confirm with the scratch test — quartz scratches glass, calcite does not — or the acid test, where calcite fizzes in dilute hydrochloric acid and quartz does not.
Does it work on cabochons and faceted stones?
Less reliably. Cutting and polishing remove habit, which is the strongest visual clue. The identifier still tries and is honest about lower confidence on cut material. Raw specimens with visible faces identify much better.
Can it handle crystal clusters and geodes?
Yes — geode interiors and clusters are some of the easiest specimens to identify because habit, color, and matrix all read at once. For a cluster, ranked matches describe the dominant crystal species and note matrix associations.
Will it tell me a crystal's spiritual or healing properties?
No. This is a geological identifier. It returns mineral identity, habit, and physical properties, not metaphysical claims.
What's a 'doubly terminated' crystal and why are they prized?
A doubly terminated crystal has points at both ends instead of one end attached to matrix. It means the crystal grew suspended in solution rather than fixed to a wall — common in vugs in dolomitic rocks. Herkimer Diamonds (a quartz variety from New York) are the best-known example.
References & sources
Property data and reference imagery used on this page are cross-checked against the following sources.
- Mindat.org
Reference for crystal habit, varietal names, and locality data.
- Smithsonian National Mineral Collection
Reference imagery for well-formed crystal habits across species.
- USGS Crystallography overview
Background on crystal systems and the geometric basis of habit.