How to Identify Minerals — What the AI Looks For

When you upload a photo to our free mineral identifier, the AI analyses the same visual properties a mineralogist would examine. Understanding these properties 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. Cubic crystals (pyrite, galena, halite) have square faces. Hexagonal prisms (quartz, beryl, apatite) are six-sided columns. Tabular crystals (barite, wulfenite) are flat plates. Acicular crystals (rutile, actinolite) are needle-like. Botryoidal forms (malachite, goethite) look like bunches of grapes. The overall form is often the strongest first clue.

Cleavage and Fracture

Cleavage is the tendency of a mineral to break along flat planes determined by its crystal structure. Calcite has rhombohedral cleavage (three directions not at 90°). Feldspar has two cleavage directions at 90°. Mica cleaves into thin flexible sheets. Quartz has no cleavage — it shows conchoidal (curved) fracture instead. Cleavage visible in a close-up photo is highly diagnostic.

Luster

Luster describes how light reflects from a mineral surface. Main categories: metallic (pyrite, galena, hematite), adamantine (diamond-like — diamond, zircon, cerussite), vitreous/glassy (quartz, calcite, fluorite), pearly (talc, some feldspars), silky (gypsum, tiger’s eye), resinous (sphalerite, amber), dull/earthy (kaolinite, limonite). Luster is best assessed dry in natural light.

Colour and Streak

Colour alone is unreliable — many minerals share similar hues. However, streak colour (the powder left on unglazed porcelain) is far more consistent. Pyrite leaves a black streak despite its golden appearance; hematite leaves red-brown; malachite leaves green. Always mention streak colour in your notes if you’ve done the test.

Mineral Identification Tests You Can Do at Home

While our AI works from photos alone, these field tests dramatically improve accuracy when you add results in the notes field.

The Streak Test

Rub the mineral across unglazed porcelain (the back of a ceramic tile). The streak colour is often different from the surface colour and far more reliable. Pyrite: black streak. Hematite: red-brown. Galena: lead-grey. Malachite: green. This test takes 10 seconds and is one of the most useful field tests available.

The Acid Test

A drop of white vinegar causes immediate fizzing on carbonate minerals — calcite, aragonite, dolomite, malachite, and azurite. Dolomite reacts only when scratched or powdered. This definitively confirms or eliminates carbonates instantly. Always test an inconspicuous spot.

The Scratch Test (Mohs Hardness)

Your fingernail is Mohs 2.5, a copper coin is Mohs 3.5, a steel knife is Mohs 5.5, and glass is Mohs 5.5–6. Talc is Mohs 1; diamond is Mohs 10. Knowing whether your specimen scratches glass immediately narrows the possibilities. Quartz (Mohs 7) scratches glass easily; calcite (Mohs 3) does not.

The Magnet Test

Magnetite is strongly magnetic. Pyrrhotite is weakly to strongly magnetic. Most other minerals are non-magnetic. Hematite is sometimes weakly attracted to a strong magnet despite not being magnetic itself. Magnetic response rules out or confirms several iron-bearing minerals instantly.

Common Minerals and How to Identify Them

These are the minerals people most frequently upload to our identifier:

Pyrite (Fool’s Gold)

Iron sulfide with a brassy golden colour and metallic luster. Forms perfect cubic or pyritohedral crystals. Hard (Mohs 6–6.5), brittle. Black streak. Often confused with gold — use our gold identifier to compare. Very common in sedimentary and hydrothermal deposits.

Quartz

The most common mineral in Earth’s crust. Hexagonal prisms with six-sided pyramid terminations. Colourless when pure; impurities produce amethyst (purple), citrine (yellow), rose quartz (pink), and smoky quartz (grey). Mohs 7, conchoidal fracture, no cleavage, vitreous luster.

Calcite

Calcium carbonate with rhombohedral cleavage and vitreous luster. Fizzes immediately with vinegar. Occurs in many colours — clear, white, yellow, orange, green, blue, pink. Often forms scalenohedral (dogtooth) crystals. Mohs 3. Fluoresces red under UV in some specimens.

Galena

Lead sulfide — the primary ore of lead. Cubic crystals with metallic luster and high density (very heavy for size). Lead-grey colour and streak. Soft (Mohs 2.5). Often found with sphalerite and pyrite in hydrothermal veins.

Hematite

Iron oxide — metallic grey to black with red-brown streak. Often botryoidal (grape-like) or specular (sparkly) form. Dense and heavy. May be weakly magnetic. Red ochre pigment comes from powdered hematite. Mohs 5.5–6.5.

Fluorite

Forms cubic or octahedral crystals in almost every colour. Glassy luster, often transparent. Mohs 4. Many specimens fluoresce blue or purple under UV light. Often found with quartz and other minerals in hydrothermal veins. Use our fluorite identifier for targeted analysis.

Where to Find Interesting Minerals

• Old mine dumps and tailings — waste rock from historical mining often contains visually striking specimens discarded as commercially unimportant.
• Quartz veins in rock outcrops — hydrothermal veins carry a wide variety of minerals including pyrite, galena, fluorite, and calcite.
• Beaches and riverbeds — water erosion concentrates harder minerals. Pebble beaches can yield quartz, agate, jasper, and garnet.
• Rock and mineral shows — dealers often sell unidentified or mislabelled specimens ideal for testing our identifier.
• Road cuts and construction sites — fresh rock faces expose minerals not visible on weathered surfaces.
• Geode and crystal shops — upload photos of specimens before buying to verify identification.

Using Our Specialist Identifier Tools

The general mineral identifier works for any mineral specimen. For specific varieties, use our specialist tools: gold identifier (gold vs pyrite), fluorite identifier, malachite identifier, garnet identifier, and 25+ more. For raw rocks rather than individual minerals, use our rock identifier.