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Mineral identification key: identify common minerals by hardness, streak, lustre, cleavage and simple tests

An interactive key to about 50 common rock-forming and ore minerals. Enter what you see (Mohs hardness or scratch tests, specific gravity, lustre, streak, cleavage, colour, acid fizz, magnetism and other simple tests) and get ranked matches with the reasons for and against each, adjustable tolerances, and a printable property table.

Keep it one tap away for everyday use.

Observe
Tolerance
Matches
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What you see

Hardness from Mohs hardness Specific gravity Lustre Streak (powder on unglazed tile) Cleavage Colour

Specific gravity from two weighings

Weight in air (g) Weight hanging in water (g)

SG = weight in air ÷ (weight in air − weight in water). Fill both to fill in the specific gravity.

Simple tests

Fizzes in cold dilute acid Fizzes when powdered Strongly magnetic Weakly magnetic Splits into thin sheets Greasy or soapy feel Striations on cleavage faces Dissolves in water Double image through a clear piece

Acid test: a drop of cold dilute hydrochloric acid (about 5 to 10 %; vinegar works slowly), with eye protection and gloves; rinse afterwards. Powder for the "fizzes when powdered" test by scratching. Never taste minerals.

How strict

Hardness counts as near within Specific gravity matches within Allow mismatches Minerals

Best matches

Each observation scores 1 if it fits the mineral's usual range, ½ if it is close (a near hardness or specific gravity, or a neighbouring lustre, streak or cleavage), and 0 if it does not fit. Real specimens vary, so check the top few against a field guide. Property values are rounded general facts.

Data

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All minerals in the key

Mineral	Formula	H	SG	Lustre	Streak	Cleavage	Colours	Tests and notes
Quartz	SiO₂	7	2.6–2.7	vitreous, greasy	white	none seen (fracture only)	colourless, white, grey, pink, purple, brown, black, yellow	Conchoidal fracture, six-sided crystals; scratches glass easily.
Orthoclase (K-feldspar)	KAlSi₃O₈	6	2.5–2.6	vitreous, pearly	white	2 directions at about 90°	pink, white, orange, grey	Two cleavages at about 90°; often pink in granite; no striations.
Microcline	KAlSi₃O₈	6–6.5	2.5–2.6	vitreous	white	2 directions at about 90°	pink, white, green	K-feldspar; green variety is amazonite; may show a cross-hatched texture.
Plagioclase feldspar	(Na,Ca)(Al,Si)₄O₈	6–6.5	2.6–2.8	vitreous, pearly	white	2 directions at about 90°	white, grey, colourless	striations on cleavage faces. Fine parallel striations on one cleavage face; some show a blue play of colour.
Muscovite (white mica)	KAl₂(AlSi₃O₁₀)(OH)₂	2–3	2.7–2.9	vitreous, pearly	white	1 direction (sheets or flat flakes)	colourless, silvery, brown, yellow	splits into thin sheets. Peels into thin, clear, elastic sheets.
Biotite (black mica)	K(Mg,Fe)₃(AlSi₃O₁₀)(OH)₂	2.5–3	2.8–3.3	vitreous, pearly, submetallic	white, grey	1 direction (sheets or flat flakes)	black, brown, green	splits into thin sheets. Peels into thin, dark, elastic sheets.
Chlorite	(Mg,Fe)₅Al(AlSi₃O₁₀)(OH)₈	2–2.5	2.6–3.3	vitreous, pearly	white, green	1 direction (sheets or flat flakes)	green	splits into thin sheets. Green, soft flakes that bend but do not spring back.
Hornblende (amphibole)	Ca₂(Mg,Fe)₄Al(Si₇Al)O₂₂(OH)₂	5–6	3–3.4	vitreous	white, grey, green	2 directions not at 90° (about 60° and 120°)	black, green, brown	Two cleavages at about 56° and 124°; long prismatic crystals.
Augite (pyroxene)	(Ca,Na)(Mg,Fe,Al)(Si,Al)₂O₆	5.5–6	3.2–3.6	vitreous	white, grey, green	2 directions at about 90°	black, green, brown	Two cleavages at about 87° and 93°; stubby crystals.
Olivine	(Mg,Fe)₂SiO₄	6.5–7	3.2–4.4	vitreous	white	none seen (fracture only)	green, yellow, brown	Olive-green glassy grains, often in basalt; conchoidal fracture.
Garnet	e.g. Fe₃Al₂(SiO₄)₃	6.5–7.5	3.5–4.3	vitreous, resinous	white	none seen (fracture only)	red, brown, pink, orange, green, black	Ball-like 12- or 24-sided crystals in metamorphic rocks.
Tourmaline	complex borosilicate	7–7.5	3–3.3	vitreous	white	none seen (fracture only)	black, green, pink, brown, blue	Long crystals with a rounded triangle cross-section and lengthwise grooves.
Kyanite	Al₂SiO₅	4.5–7	3.5–3.7	vitreous, pearly	white	1 direction (sheets or flat flakes)	blue, white, grey, green	Bladed blue crystals; softer along the blade than across it.
Sillimanite	Al₂SiO₅	6.5–7.5	3.2–3.3	vitreous, silky	white	1 direction (sheets or flat flakes)	white, brown, grey	Fibrous or needle-like masses in high-grade metamorphic rocks.
Andalusite	Al₂SiO₅	6.5–7.5	3.1–3.2	vitreous	white	2 directions at about 90°	pink, brown, grey, red	Square prisms; the chiastolite variety shows a dark cross.
Staurolite	Fe₂Al₉Si₄O₂₃(OH)	7–7.5	3.7–3.8	vitreous, resinous	white, grey	none seen (fracture only)	brown, red, black	Brown prisms, often crossed twins, in schist.
Epidote	Ca₂(Al,Fe)₃(SiO₄)₃(OH)	6–7	3.3–3.5	vitreous	white, grey	1 direction (sheets or flat flakes)	green, yellow	Pistachio-green crystals or masses.
Calcite	CaCO₃	3	2.7	vitreous	white	3 directions not at 90° (rhombs)	colourless, white, grey, yellow, pink, orange, green, blue	fizzes in cold dilute acid. double image through a clear piece. Breaks into rhombs; fizzes in cold dilute acid; clear pieces show double images.
Dolomite	CaMg(CO₃)₂	3.5–4	2.8–2.9	vitreous, pearly	white	3 directions not at 90° (rhombs)	white, pink, grey, brown	fizzes when powdered. Like calcite but fizzes in cold dilute acid only when powdered; often curved crystal faces.
Gypsum	CaSO₄·2H₂O	2	2.3	vitreous, pearly, silky	white	1 direction (sheets or flat flakes)	colourless, white, grey, pink, brown	Scratched by a fingernail; clear selenite, fibrous satin spar.
Halite (rock salt)	NaCl	2.5	2.1–2.2	vitreous	white	3 directions at 90° (cubes)	colourless, white, pink, grey	dissolves in water. Cubic cleavage; dissolves in water.
Fluorite	CaF₂	4	3.1–3.2	vitreous	white	4 directions (octahedra)	purple, green, yellow, colourless, blue	Cubes; cleaves into octahedra (four directions).
Apatite	Ca₅(PO₄)₃(F,Cl,OH)	5	3.1–3.2	vitreous, resinous	white	none seen (fracture only)	green, blue, brown, yellow	Six-sided prisms; Mohs 5, just scratched by a knife.
Talc	Mg₃Si₄O₁₀(OH)₂	1	2.7–2.8	pearly, greasy	white	1 direction (sheets or flat flakes)	white, green, grey	greasy or soapy feel. Very soft, soapy feel; Mohs 1.
Kaolinite (clay)	Al₂Si₂O₅(OH)₄	2–2.5	2.6	earthy	white	none seen (fracture only)	white, yellow	Soft white earthy masses; clay smell when breathed on.
Serpentine	(Mg,Fe)₃Si₂O₅(OH)₄	2.5–5	2.5–2.6	greasy, silky	white	none seen (fracture only)	green, yellow, black	greasy or soapy feel. Mottled green, greasy to waxy look; some forms fibrous.
Topaz	Al₂SiO₄(F,OH)₂	8	3.5–3.6	vitreous	white	1 direction (sheets or flat flakes)	colourless, yellow, blue, brown, pink	Mohs 8; one perfect cleavage across the prism.
Corundum	Al₂O₃	9	3.9–4.1	adamantine, vitreous	white	none seen (fracture only)	grey, brown, red, blue, pink	Mohs 9; barrel-shaped six-sided crystals; ruby and sapphire.
Barite	BaSO₄	3–3.5	4.3–4.6	vitreous, pearly	white	3 directions not at 90° (rhombs)	white, colourless, grey, blue, brown	Feels very heavy for a light-coloured mineral.
Siderite	FeCO₃	3.5–4.5	3.7–3.9	vitreous, pearly	white	3 directions not at 90° (rhombs)	brown, yellow, grey	fizzes when powdered. Brown rhombs; fizzes slowly in warm or powdered acid tests.
Magnetite	Fe₃O₄	5.5–6.5	5.1–5.2	metallic	black	none seen (fracture only)	black, metal-grey	strongly magnetic. Strongly attracted to a magnet; octahedral crystals.
Hematite	Fe₂O₃	5–6.5	4.9–5.3	metallic, submetallic, earthy	red-brown, red	none seen (fracture only)	metal-grey, black, red, brown	Red-brown streak even when the specimen is steel grey.
Goethite (limonite)	FeO(OH)	4–5.5	3.3–4.3	submetallic, earthy, silky	yellow-brown, brown	none seen (fracture only)	brown, yellow, black	Yellow-brown streak; rusty earthy masses (limonite).
Ilmenite	FeTiO₃	5–6	4.5–5	metallic, submetallic	black, brown	none seen (fracture only)	black, metal-grey	weakly magnetic. Black, weakly magnetic; common in black sands.
Chromite	FeCr₂O₄	5.5	4.5–5.1	metallic, submetallic	brown	none seen (fracture only)	black	weakly magnetic. Black with a dark brown streak; in ultramafic rocks.
Pyrite	FeS₂	6–6.5	4.9–5.2	metallic	greenish-black, black	none seen (fracture only)	brassy	"Fool’s gold": pale brass, hard, cubes with striated faces.
Chalcopyrite	CuFeS₂	3.5–4	4.1–4.3	metallic	greenish-black	none seen (fracture only)	brassy, gold	Deeper brass-yellow than pyrite, softer (a knife scratches it), often tarnished.
Pyrrhotite	Fe₁₋ₓS	3.5–4.5	4.6–4.7	metallic	grey, black	none seen (fracture only)	brassy, brown	weakly magnetic. Bronze colour; weakly magnetic.
Galena	PbS	2.5	7.4–7.6	metallic	grey, black	3 directions at 90° (cubes)	metal-grey	Very heavy, lead grey, cubic cleavage.
Sphalerite	ZnS	3.5–4	3.9–4.1	resinous, adamantine, submetallic	yellow-brown, white, brown, yellow	6 directions	brown, yellow, black, red	Resinous lustre, six cleavage directions, pale streak despite a dark colour.
Cinnabar	HgS	2–2.5	8–8.2	adamantine, submetallic	red	3 directions not at 90° (rhombs)	red	Scarlet streak, very heavy. Contains mercury: wash hands, do not heat.
Stibnite	Sb₂S₃	2	4.6	metallic	grey, black	1 direction (sheets or flat flakes)	metal-grey	Long lead-grey blades with one perfect lengthwise cleavage.
Molybdenite	MoS₂	1–1.5	4.6–4.8	metallic	grey, greenish-black	1 direction (sheets or flat flakes)	metal-grey, blue	splits into thin sheets. greasy or soapy feel. Like graphite but bluish and heavier; flexible sheets.
Graphite	C	1–2	2.1–2.3	metallic, submetallic	black, grey	1 direction (sheets or flat flakes)	black, metal-grey	greasy or soapy feel. splits into thin sheets. Marks paper; greasy feel; light for a metallic mineral.
Arsenopyrite	FeAsS	5.5–6	5.9–6.2	metallic	grey, black	none seen (fracture only)	silvery, metal-grey	Silver-white, striated prisms. Contains arsenic: wash hands.
Cassiterite	SnO₂	6–7	6.8–7.1	adamantine, submetallic	white, yellow-brown, brown	none seen (fracture only)	brown, black	Hard, very heavy, dark brown with a pale streak; tin ore.
Malachite	Cu₂CO₃(OH)₂	3.5–4	3.6–4	silky, vitreous, earthy	green	none seen (fracture only)	green	fizzes in cold dilute acid. Banded bright green; fizzes in dilute acid.
Azurite	Cu₃(CO₃)₂(OH)₂	3.5–4	3.7–3.9	vitreous, earthy	blue	none seen (fracture only)	blue	fizzes in cold dilute acid. Deep blue, often with malachite; fizzes in dilute acid.
Native copper	Cu	2.5–3	8.9	metallic	copper	none seen (fracture only)	copper, brown, green	Copper-red, bends, hackly fracture; green tarnish.
Native gold	Au	2.5–3	15–19.3	metallic	gold	none seen (fracture only)	gold	Gold-yellow streak, soft, bends, extremely heavy; does not tarnish.
Native sulfur	S	1.5–2.5	2–2.1	resinous, greasy	white, yellow	none seen (fracture only)	yellow	Bright yellow, light, brittle; smells when burned (do not burn it).

Rounded general values written by fibub from general mineralogy knowledge; specimens vary. H = Mohs hardness, SG = specific gravity.

What it does

This is a mineral identification key for hand specimens. It holds about 50 common minerals: the main rock-forming silicates (quartz, feldspars, micas, amphibole, pyroxene, olivine, garnet and more), carbonates, sulfates, halides, and common ore minerals (magnetite, hematite, pyrite, chalcopyrite, galena, sphalerite, cassiterite, native metals and others). For each it knows rounded, general values: Mohs hardness range, specific gravity range, lustre, streak, cleavage, usual colours and simple tests (fizzing in dilute acid, magnetism, thin sheets, greasy feel, striations, dissolving in water, double refraction).

You tell it what you see. Every mineral is scored against each observation: 1 if it fits, ½ if it is close, 0 if it does not. The page lists the best matches with ✓, ≈ and ✗ for each reason, so you can see why a mineral is (or is not) suggested. A full property table can be printed or saved as CSV.

How to use it

Hardness: type a Mohs number, or choose a scratch test: a fingernail scratches it (under 2.5), a copper coin does (2.5 to 3.5), a steel knife or glass does (3.5 to 5.5), or it scratches glass (over 5.5).
Streak: rub the mineral on the back of an unglazed tile and look at the powder’s colour. It is much more reliable than the mineral’s colour.
Lustre: metallic, submetallic or one of the non-metallic kinds (vitreous is glassy).
Cleavage: count the flat breaking directions and the angles between them.
Specific gravity (optional): type it, or weigh the specimen in air and hanging in water; SG = air ÷ (air − water).
Tests: answer yes or no only for tests you did. “No” counts too: a mineral that should fizz but did not gets a ✗.
How strict: widen the hardness or SG tolerance, or allow one or two mismatches, if your observations are rough.

Worked example

A white, glassy specimen with hardness 3, white streak, rhomb-shaped cleavage (three directions not at 90°) that fizzes in cold dilute acid: Calcite scores 5 of 5. Next come Barite (4 of 5: it does not fizz), then Dolomite and Siderite (3½ of 5: hardness is half a step off and they fizz only when powdered). Change the acid test to “no” and “fizzes when powdered” to “yes”, with hardness 3.5, and Dolomite moves to the top.

Tips

Use a fresh surface: weathered skins change colour, lustre and hardness.
Colour misleads (quartz comes in many), so leave it as “any” unless it is distinctive, like malachite green.
A dark mineral with a pale streak is often sphalerite; a grey metallic mineral with a red-brown streak is hematite.
Some minerals here contain toxic elements (cinnabar, arsenopyrite, galena): wash your hands after handling.

FAQ

How accurate are the values? They are rounded general facts for typical specimens; real minerals vary with composition. Use the matches as a short list and confirm with a field guide or a teacher.

Can it identify rocks? No, only minerals. Rocks are mixtures; identify their minerals first.

Is my data stored? No. Everything runs in this page.

Where the numbers come from

Property values are rounded general facts written by fibub from general mineralogy knowledge, as taught in standard textbooks such as Klein and Philpotts, Earth Materials (Cambridge University Press), and Nesse, Introduction to Mineralogy (Oxford University Press). No tables were copied.
Mohs hardness scale (Mohs 1812) and the common field references: fingernail about 2.5, copper coin about 3.5, steel knife and glass about 5.5.

Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.

Last updated 2026-11-09.