How to Identify Minerals: The 7 Tests That Name Any Specimen

There are thousands of named minerals, but you do not identify one by memorizing them — you identify it by running a short, repeatable checklist of physical properties and letting the answers converge on a name. With a porcelain tile, a steel knife, a magnet, and ten minutes, you can identify the overwhelming majority of minerals you will ever find.

First: is it even a mineral?

A mineral is a naturally occurring, inorganic solid with a fixed chemical formula and an ordered internal structure. A rock is an aggregate of mineral grains. If your specimen is a mix of different-colored grains cemented together, you are holding a rock — name its minerals first, then read our rock identification guide. If it is a single uniform substance, run the seven tests below.

The seven tests

1. Hardness

Start here — it eliminates the most candidates fastest. Using the Mohs scratch test, find whether your specimen is scratched by a fingernail (~2.5), a coin (~3.5), a knife (~5.5), or whether it scratches glass (6+). "Harder or softer than quartz (7)?" is the master fork.

2. Streak

Drag the specimen across an unglazed porcelain tile and look at the powder color. Streak strips away the deception of surface color: hematite streaks rust-red no matter what it looks like; pyrite streaks greenish-black; galena streaks lead-gray. Most non-metallic minerals streak white or colorless — itself a useful result.

3. Luster

How does the surface reflect light? The big division is metallic (looks like polished metal — pyrite, galena, magnetite) versus non-metallic. Non-metallic lusters have their own vocabulary: vitreous (glassy, like quartz), pearly (mica), silky (fibrous gypsum), resinous, earthy (dull, like chalk), and adamantine (brilliant, like diamond).

4. Color

Note it — but trust it least. Color is diagnostic for a few minerals (malachite is always green, azurite always deep blue) but misleading for many. Record it as a supporting clue, never the deciding one.

5. Cleavage and fracture

Break or examine an edge. Does it split along flat planes (cleavage) or into curved/irregular surfaces (fracture)?

• Mica — one perfect cleavage; peels into thin sheets.
• Feldspar — two cleavages at ~90°; stair-step faces.
• Halite / galena — three cleavages at 90°; breaks into cubes.
• Calcite — three cleavages not at 90°; breaks into leaning rhombs.
• Quartz — no cleavage; conchoidal fracture only.

Counting planes and estimating their angles is often the single most decisive test.

6. Crystal form

If the mineral grew into open space, its outward shape reflects its internal structure: quartz's six-sided prisms, pyrite's cubes, garnet's rounded 12-sided balls. Well-formed crystals are a gift — most minerals grow crammed against neighbors and show no faces, which is why the other tests matter. Learn the vocabulary in our crystal identification guide.

7. Special tests

A handful of quick checks clinch specific minerals:

• Magnetism — magnetite tugs a magnet; some pyrrhotite is weakly magnetic.
• Acid fizz — a drop of vinegar or dilute acid makes calcite effervesce vigorously; dolomite fizzes only when powdered.
• Heft (specific gravity) — galena and barite feel startlingly heavy for their size; pumice floats.
• Feel and smell — talc feels greasy; some sulfides smell of rotten egg when scratched.

Putting it together: a worked example

A specimen is brassy gold, opaque, and shiny — is it gold? Run the tests. It is hard (a knife barely marks it — gold is soft, ~2.5), it streaks greenish-black (gold streaks yellow), and it forms cubes (gold does not). Verdict: pyrite, "fool's gold." One streak test settles a question that fools people every week — see the full breakdown in pyrite vs. gold.

A repeatable habit

Run the tests in the same order every time — hardness, streak, luster, color, cleavage, form, special — and record each answer. The list is short enough to memorize, and the discipline of always checking streak before trusting color is what separates a confident identification from a lucky guess. When you want a second opinion in the field, a photo-based ID is a fast cross-check, but the seven tests are what let you understand the answer.