Physical-property field guide
Move beyond color. Compare hardness, streak, luster, cleavage, fracture, density, magnetism, and geologic setting to identify common minerals with greater confidence.
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Use converging evidence
Observe first, test gently, and verify with at least two independent properties. Mixed grains, coatings, alteration, and weathering can change the result.
Learn the field-test proceduresNeed help narrowing the possibilities? Use the interactive identifier. If the grains form a mixed material, begin with the rock identification guides.
Foundation collection
Silicate mineral · SiO₂Quartz is a common, hard, glassy mineral with no cleavage and conchoidal fracture; its many colors make physical tests more reliable than appearance alone.
Carbonate mineral · CaCO₃Calcite is a relatively soft carbonate mineral recognized by Mohs hardness 3, three-direction rhombohedral cleavage, and vigorous reaction with dilute acid on a fresh surface.
Sulfate mineral · CaSO₄·2H₂OGypsum is a very soft hydrous sulfate mineral that can be scratched by a fingernail and occurs as clear crystals, white fibrous masses, rosettes, or massive alabaster.
Halide mineral · NaClHalite is natural sodium chloride, typically recognized by cubic crystals or three perfect cleavage directions at right angles, softness, and ready solubility in water.
Halide mineral · CaF₂Fluorite is a colorful mineral defined by Mohs hardness 4, glassy luster, and four perfect cleavage directions that can produce octahedral fragments.
Silicate mineral groupFeldspar is a family of abundant rock-forming silicates generally identified by hardness near 6, two cleavage directions, and blocky crystals; precise species identification may require optical or chemical work.
Light-colored mica mineralMuscovite is a pale mica that splits into thin, flexible, elastic sheets with a pearly to glassy luster and is commonly colorless, silvery, tan, or pale green.
Dark mica mineral groupBiotite is the common field name for dark iron- and magnesium-rich mica, recognized by perfect sheet cleavage, flexible elastic flakes, and brown to black color.
Sulfide mineral · FeS₂Pyrite is a brassy iron sulfide commonly called fool’s gold; it is harder and more brittle than gold, produces a dark streak, and often forms striated cubes.
Iron oxide mineral · Fe₂O₃Hematite is an iron oxide whose most reliable field clue is a red to reddish-brown streak, even when the specimen itself looks steel gray, black, earthy, or red.
Iron oxide mineral · Fe₃O₄Magnetite is a black iron oxide readily recognized by strong attraction to a magnet, black streak, relatively high density, and commonly octahedral or granular form.
Silicate mineral groupOlivine is an olive-green to yellow-green rock-forming silicate, usually granular, hard, glassy, and lacking good cleavage; gem-quality material is called peridot.
Silicate mineral groupGarnet is a group of hard silicate minerals that commonly forms equant, many-faced crystals with no cleavage; red is common, but garnet also occurs in orange, green, brown, black, and other colors.
Native element · AuNative gold is a dense, soft, malleable yellow metal that bends or flattens instead of shattering and leaves a yellow streak; those properties separate it from pyrite and most glittering minerals.
Copper iron sulfide · CuFeS₂Chalcopyrite is a brass-yellow copper iron sulfide that is softer and usually deeper yellow than pyrite, commonly tarnishes purple or blue, and leaves a greenish-black streak.
Native element · CDiamond is crystalline carbon defined by Mohs hardness 10, adamantine luster, high thermal conductivity, and perfect octahedral cleavage, but rough crystals and common imitations usually require professional testing.
Sheet silicate · Mg₃Si₄O₁₀(OH)₂Talc is the softest standard mineral at Mohs hardness 1, recognized by its very easy scratch, greasy or soapy feel, pale color, and platy to massive habit.
Carbonate mineral · CaMg(CO₃)₂Dolomite is a calcium-magnesium carbonate with rhombohedral cleavage and hardness about 3.5 to 4; unlike calcite, an unpowdered fresh surface usually reacts weakly with cold dilute acid.
Native element · CuNative copper is a soft, malleable metallic mineral with a fresh copper-red color, high density, and no cleavage; exposed surfaces commonly tarnish brown, black, or green.
Native element · AgNative silver is a dense, soft, malleable metal with a bright silver-white fresh surface that commonly tarnishes gray, brown, or black; it occurs in wires, plates, grains, and irregular masses.
Lead sulfide · PbSGalena is a dense, metallic lead-gray sulfide recognized by perfect cubic cleavage, a gray to black streak, and unusual heft; it is also a lead-bearing mineral that requires careful handling.
Zinc sulfide · ZnSSphalerite is the principal zinc sulfide, recognized by resinous to adamantine luster, pale yellow to dark brown or black color, perfect cleavage in six directions, and a light-colored streak that may smell sulfurous when freshly scratched.
Aluminum oxide · Al₂O₃Corundum is a very hard aluminum oxide mineral with Mohs hardness 9, no cleavage, and commonly barrel-shaped or tabular crystals; transparent red material is ruby and other gem colors are sapphire.
Native element · CGraphite is a very soft, opaque form of carbon recognized by its dark gray color, greasy feel, perfect basal cleavage, low density, and black mark on paper or porcelain.
Molybdenum disulfide · MoS₂Molybdenite is a soft, dense, bluish-silver sulfide with a greasy feel and perfect basal cleavage; its flexible flakes resemble graphite but are substantially heavier and usually lighter in color.
Native element · SNative sulfur is a very soft, lightweight, bright yellow nonmetallic mineral with a resinous luster, pale streak, and brittle fracture; it is commonly associated with volcanic gases, evaporites, and sulfide oxidation.
Copper carbonate hydroxide · Cu₂CO₃(OH)₂Malachite is a vivid green copper carbonate hydroxide commonly recognized by its green streak, banded or botryoidal forms, and occurrence in oxidized copper deposits.
Copper carbonate hydroxide · Cu₃(CO₃)₂(OH)₂Azurite is a deep blue copper carbonate hydroxide identified by its blue streak, glassy to earthy luster, softness, and occurrence with other oxidized copper minerals such as malachite.
Phosphate mineral group · Ca₅(PO₄)₃(F,Cl,OH)Apatite is a calcium phosphate mineral group used as Mohs hardness 5, commonly recognized by hexagonal crystals, glassy luster, variable color, and hardness between fluorite and feldspar.
Aluminum silicate fluoride hydroxide · Al₂SiO₄(F,OH)₂Topaz is a hard aluminum silicate mineral identified by Mohs hardness 8, perfect basal cleavage, glassy luster, and commonly prismatic orthorhombic crystals.
Beryllium aluminum silicate · Be₃Al₂Si₆O₁₈Beryl is a hard beryllium aluminum silicate commonly forming six-sided prisms; gem varieties include emerald and aquamarine, but most beryl is pale, cloudy, or opaque.
Complex borosilicate mineral groupTourmaline is a diverse borosilicate mineral group commonly recognized by hard, strongly lengthwise-striated prismatic crystals with triangular to rounded-triangular cross sections.
Clay mineral · Al₂Si₂O₅(OH)₄Kaolinite is a soft white to pale clay mineral commonly occurring as earthy, powdery, or compact masses; reliable identification often requires laboratory methods because individual crystals are microscopic.
Amphibole-group mineralHornblende is a dark amphibole-group mineral commonly identified by elongate prismatic crystals, two good cleavage directions meeting near 56 and 124 degrees, and occurrence in igneous and metamorphic rocks.
Clinopyroxene-group mineralAugite is a dark calcium-rich clinopyroxene commonly recognized by short blocky prisms, two cleavage directions close to 90 degrees, Mohs hardness near 5.5 to 6, and occurrence in mafic igneous rocks.
Hydrous magnesium silicate mineral groupSerpentine is a group of soft green to yellowish hydrous magnesium silicate minerals with greasy, waxy, silky, or fibrous appearances; some fibrous varieties are regulated asbestos minerals.
Hydrous sheet-silicate mineral groupChlorite is a group of commonly green, soft sheet silicates recognized by perfect basal cleavage, flexible but generally nonelastic flakes, and widespread occurrence in low-grade metamorphic and altered rocks.
Calcium aluminum iron sorosilicate · Ca₂(Al,Fe)₃(SiO₄)₃(OH)Epidote is commonly a pistachio-green to yellow-green mineral with prismatic habit, glassy luster, one perfect cleavage, and hardness near 6 to 7, widespread in metamorphic and altered rocks.
Barium sulfate · BaSO₄Barite is a notably heavy, relatively soft barium sulfate mineral commonly recognized by high density, white streak, tabular or bladed crystals, and hardness near 3 to 3.5.
Strontium sulfate · SrSO₄Celestite is a strontium sulfate mineral commonly found as pale blue, white, or colorless tabular crystals with high density, white streak, good cleavage, and hardness near 3 to 3.5.
Aluminum silicate · Al₂SiO₅Kyanite is a bladed aluminum silicate mineral with strongly directional hardness, commonly blue to gray, that forms in aluminum-rich metamorphic rocks at elevated pressure.
Iron magnesium aluminum silicate hydroxideStaurolite is a brown to reddish-brown metamorphic mineral known for prismatic crystals and distinctive cross-shaped twins, with hardness near 7 to 7.5 and a pale streak.
Iron oxide hydroxide · FeO(OH)Goethite is a brown to yellow-brown iron oxide hydroxide identified by its yellowish-brown streak, earthy to submetallic luster, and common botryoidal, fibrous, stalactitic, or earthy habits.
Titanium dioxide · TiO₂Rutile is a dense titanium dioxide mineral commonly identified by reddish-brown to black prismatic crystals, strong lengthwise striations, high luster, hardness near 6 to 6.5, and a pale brown streak.
Iron titanium oxide · FeTiO₃Ilmenite is a dense black to brownish-black iron titanium oxide recognized by its submetallic luster, black to brownish-red streak, weak or variable magnetism, and common occurrence in mafic rocks and heavy-mineral sands.
Zirconium silicate · ZrSiO₄Zircon is a dense, hard zirconium silicate identified by tetragonal prismatic crystals, high luster, hardness near 7.5, and colors ranging from colorless to brown, red, yellow, green, or blue.
Tin oxide · SnO₂Cassiterite is a very dense tin oxide identified by hardness near 6 to 7, brown to black color, adamantine to submetallic luster, pale streak, and common short prismatic or bipyramidal crystals.
Rare-earth phosphate mineral group · (Ce,La,Nd,Th)PO₄Monazite is a dense yellow-brown to reddish-brown rare-earth phosphate mineral, commonly occurring as resinous accessory crystals or heavy sand grains and often containing naturally occurring thorium and uranium.
Common lookalikes
Compare two possible minerals using the properties that actually separate them—hardness, streak, cleavage, magnetism, acid response, and crystal form.
