How to Identify Crystals — What the AI Looks For

When you upload a photo to our free crystal identifier, the AI analyses the same visual properties a mineralogist would examine. Understanding what these properties are helps you take better photos and interpret your results more confidently.

Crystal Habit and Form

Crystal habit describes the typical shape a mineral grows in. Prismatic crystals are elongated columns (quartz, tourmaline). Tabular crystals are flat and plate-like (barite, wulfenite). Acicular crystals are needle-like (rutile, actinolite). Massive specimens have no visible crystal faces. Botryoidal forms look like bunches of grapes (malachite, goethite). The overall form is often the strongest first clue.

Terminations and Crystal Faces

Terminations are the pointed or flat ends of a crystal where growth stopped. Quartz typically shows six-sided pyramids; calcite shows rhombohedral faces; fluorite shows cubic or octahedral faces. The number, shape, and symmetry of faces reveal the underlying crystal system — and our AI is trained to recognise these patterns from close-up photographs.

Colour, Zoning, and Phantoms

Colour alone is not always reliable — many crystals share similar hues. However, colour zoning (bands or patches of different colour within one crystal) and phantoms (ghost-like outlines of earlier growth stages visible inside) are highly diagnostic. Amethyst often shows colour zoning from pale to deep purple; citrine can be heat-treated amethyst with an orange gradient.

Transparency, Clarity, and Inclusions

Transparency ranges from transparent (light passes through clearly) to translucent (light diffused) to opaque (no light passes). Internal inclusions — bubbles, needles, veils, or other minerals trapped during growth — help distinguish natural crystals from glass and synthetic stones. Glass typically shows round bubbles; natural crystals show angular mineral inclusions.

Luster

Luster describes how light reflects from a crystal surface. Main categories: vitreous or glassy (quartz, fluorite, calcite), adamantine (diamond-like brilliance — zircon, cerussite), pearly (soft iridescent sheen — talc, some feldspars), silky (parallel fibre sheen — selenite, tiger’s eye), metallic (pyrite, galena). Luster is best assessed with the crystal dry and clean in natural light.

Crystal Identification Tests You Can Do at Home

While our AI works from photos alone, providing physical test results in the notes field significantly improves your identification. These simple tests take seconds and require no specialist equipment.

The Scratch Test (Mohs Hardness)

The Mohs scale rates mineral hardness from 1 (talc) to 10 (diamond). Everyday reference points: your fingernail is approximately Mohs 2.5, a copper coin is Mohs 3.5, a steel knife blade is Mohs 5.5, and glass is Mohs 5.5–6. Quartz (Mohs 7) scratches glass easily; selenite (Mohs 2) can be scratched with a fingernail. These two data points immediately narrow down the possibilities considerably.

The UV Fluorescence Test

Many crystals glow under ultraviolet light. Fluorite often fluoresces blue or purple; calcite may glow red, pink, or orange; scheelite glows bright blue-white; hyalite opal shows green. A basic UV torch costs a few pounds and is one of the most useful tools for crystal collectors. Always mention UV response in your notes.

The Acid Test

A drop of white vinegar causes immediate fizzing on carbonate crystals — calcite, aragonite, and malachite all react visibly. Dolomite reacts only when scratched or powdered. This test definitively confirms or eliminates carbonate minerals in 10 seconds. Always test an inconspicuous spot as acid can damage polished surfaces.

The Streak Test

Rubbing a crystal across unglazed porcelain (the unfinished back of a ceramic tile) leaves a coloured powder that is often different from the surface colour. Pyrite leaves a black streak despite its golden appearance; hematite leaves a distinctive red-brown streak. Streak colour is more consistent than surface colour and helps eliminate look-alikes.

Common Crystals and How to Identify Them

These are the crystals people most frequently upload to our identifier. Understanding their key features helps you provide better information and interpret your result.

Clear Quartz

The most common crystal on Earth. Hexagonal prisms with six-sided pyramid terminations. Colourless and transparent when pure. Mohs 7 — scratches glass easily. Conchoidal fracture. No cleavage. Does not react to acid. Often found as points, clusters, or inside geodes.

Amethyst

Purple variety of quartz caused by iron impurities and natural irradiation. Same hexagonal habit as clear quartz. Colour ranges from pale lavender to deep purple, often with colour zoning. Use our dedicated amethyst identifier for the most targeted analysis. Heat-treated amethyst can look like citrine.

Rose Quartz

Pink variety of quartz, usually massive or tumbled rather than well-formed crystals. Colour from trace titanium, iron, or manganese. Translucent to opaque. Mohs 7. Often confused with pink calcite (Mohs 3, reacts to acid) or dyed glass (uniform colour, may show bubbles).

Selenite

Transparent to translucent variety of gypsum. Tabular or bladed crystals with pearly or silky luster. Very soft — Mohs 2, scratched easily with a fingernail. Often forms long wand-like crystals. Use our selenite identifier for fibrous gypsum varieties.

Fluorite

Forms cubic or octahedral crystals in almost every colour — purple, green, blue, yellow, and colourless. Glassy luster, often transparent. Mohs 4 — softer than quartz. Many specimens fluoresce under UV light. Often confused with coloured glass, which shows round bubbles instead of angular crystal faces.

Citrine

Yellow to orange variety of quartz. Natural citrine is rare; most commercial “citrine” is heat-treated amethyst. Look for colour zoning and a reddish tint at the base of natural specimens. Use our citrine identifier to distinguish natural citrine from heated amethyst.

How to Spot Fake Crystals

Fake and mislabelled crystals are common in shops, markets, and online. Here are the most frequent issues our AI checks for:

• Glass sold as crystal — round bubbles, perfectly uniform colour, mould marks, and conchoidal fracture without crystal faces are red flags.
• Dyed specimens — colour concentrated in cracks and surface pits; white or pale areas where dye did not penetrate; unnaturally vivid uniform colour.
• Heat-treated amethyst sold as citrine — orange-yellow colour with reddish zones at the base; crumbly white tips on heated points.
• Resin or plastic — warm to the touch, lightweight, may smell when scratched; no crystal faces or natural inclusions.
• Mislabelled minerals — “green amethyst” (does not exist), “blue obsidian” (usually glass), “smelt quartz” (industrial slag).
• Reconstituted stone — crushed mineral powder bonded with resin; uniform texture, no natural crystal structure, often very cheap for the claimed material.

Using Our Specialist Identifier Tools

The general crystal identifier works for any crystal specimen. But if you already suspect what you have, our specialist tools give more targeted results with AI prompts specifically tuned to that crystal’s identifying features. For faceted gems and jewellery stones, use our gemstone identifier. For rough rocks and matrix specimens, try our rock identifier or mineral identifier. For specific varieties, tools like our amethyst, fluorite, and moonstone identifiers assess treatment, authenticity, and collector value.