Oxide minerals

name colour lustre Mohs hardness specific gravity

anatase brown to indigo blue and black; also variable adamantine to metallic adamantine 5½–6 3.8–4.0

boehmite white, when pure 3 3.0–3.1

brookite various browns metallic adamantine to submetallic 5½–6 4.1–4.2

brucite white to pale green, gray, or blue waxy to vitreous 2½ 2.4

cassiterite reddish or yellowish brown to brownish black adamantine to metallic adamantine, usually splendent 6–7 7.0

chromite black metallic 5½ 4.5–4.8

chrysoberyl variable vitreous 8½ 3.6–3.8

columbite iron black to brownish black; often with iridescent tarnish 6–6½ 5.2 (columbite) to 8.0 (tantalite)

corundum red (ruby); blue (sapphire); also variable adamantine to vitreous 9 (a hardness standard) 4.0–4.1

cuprite various shades of red adamantine to earthy 3½–4 6.1

delafossite black metallic 5½ 5.4–5.5

diaspore white, grayish white, colourless; variable brilliant vitreous 6½–7 3.2–3.5

euxenite black brilliant submetallic to greasy or vitreous 5½–6½ 5.3–5.9

franklinite brownish black to black metallic to semimetallic 5½–6½ 5.1–5.2

gibbsite white; grayish, greenish, reddish white vitreous 2½–3½ 2.3–2.4

goethite blackish brown (crystals); yellowish or reddish brown adamantine-metallic 5–5½ 3.3–4.3

hausmannite brownish black submetallic 5½ 4.8

hematite steel gray; dull to bright red metallic or submetallic to dull 5–6 5.3

ilmenite iron black metallic to submetallic 5–6 4.7–4.8

lepidocrocite ruby red to reddish brown submetallic 5 4.0–4.1

litharge red greasy to dull 2 9.1–9.2

magnetite black to brownish black metallic to semimetallic 5½–6½ 5.2

manganite dark steel gray to iron black submetallic 4 4.3–4.4

massicot sulfur to orpiment yellow greasy to dull 2 9.6

periclase colourless to grayish; also green, yellow, or black vitreous 5½–6 3.6–3.7

perovskite (often containing rare earths) black; grayish or brownish black; reddish brown to yellow adamantine to metallic 5½ 4.0–4.3

psilomelane iron black to dark steel gray submetallic to dull 5–6 4.7

pyrochlore brown to black (pyro); pale yellow to brown (micro) vitreous or resinous 5–5½ 4.2–6.4

pyrolusite light steel gray to iron black metallic 2–6 4.4–5.0

rutile reddish brown to red; variable metallic adamantine 6–6½ 4.2–5.5

spinel various vitreous 7½–8 3.55

tenorite steel or iron gray to black metallic 3½ 5.8–6.4

thorianite dark gray to brownish black and bluish hornlike to submetallic 6½ 9.7–9.9

uraninite steel to velvet black; grayish, greenish submetallic to greasy or dull 5–6 6.5–8.5 (massive); 8.0–10.0 (crystals)

name habit fracture or cleavage refractive indices or polished section data crystal system

anatase pyramidal or tabular crystals two perfect cleavages omega = 2.561

epsilon = 2.488

extremely variable tetragonal

boehmite disseminated or in pisolitic aggregates one very good cleavage alpha = 1.64–1.65

beta = 1.65–1.66

gamma = 1.65–1.67 orthorhombic

brookite only as crystals, usually tabular subconchoidal to uneven fracture alpha = 2.583

beta = 2.585

gamma = 2.700–2.741 orthorhombic

brucite tabular crystals; platy aggregates; fibrous or foliated massive one perfect cleavage omega = 1.56–1.59

epsilon = 1.58–1.60 hexagonal

cassiterite repeatedly twinned crystals; crusts and concretions one imperfect cleavage omega = 1.984–2.048

epsilon = 2.082–2.140

light gray; strongly anisotropic tetragonal

chromite granular to compact massive no cleavage; uneven fracture n = 2.08–2.16

brownish gray-white; isotropic isometric

chrysoberyl tabular or prismatic, commonly twinned, crystals one distinct cleavage alpha = 1.746

beta = 1.748

gamma = 1.756 orthorhombic

columbite prismatic crystals, often in large groups; massive one distinct cleavage brownish gray-white; weakly anisotropic orthorhombic

corundum pyramidal or barrel-shaped crystals; large blocks; rounded grains no cleavage; uneven to conchoidal fracture omega = 1.767–1.772

epsilon = 1.759–1.763 hexagonal

cuprite octahedral, cubic, or capillary crystals; granular or earthy massive conchoidal to uneven fracture n = 2.849

bluish white; anomalously anisotropic and plechroic isometric

delafossite tabular crystals; botryoidal crusts one imperfect cleavage rosy brown-white; strongly anisotropic; distinctly pleochroic hexagonal

diaspore thin, platy crystals; scaly massive; disseminated one perfect cleavage, one less so alpha = 1.682–1.706

beta = 1.705–1.725

gamma = 1.730–1.752 orthorhombic

euxenite prismatic crystals; massive conchoidal to subconchoidal fracture n = 2.06–2.25 orthorhombic

franklinite octahedral crystals; granular massive n = about 2.36

white; isotropic isometric

gibbsite tabular crystals; crusts and coatings; compact earthy one perfect cleavage alpha = 1.56–1.58

beta = 1.56–1.58

gamma = 1.58–1.60 monoclinic

goethite prismatic crystals; massive one perfect cleavage, one less so alpha = 2.260–2.275

beta = 2.393–2.409

gamma = 2.398–2.515

gray; strongly anisotropic orthorhombic

hausmannite pseudo-octahedral crystals; granular massive one nearly perfect cleavage omega = 2.43–2.48

epsilon = 2.13–2.17

gray-white; distinctly anisotropic tetragonal

hematite tabular crystals; rosettes; columnar or fibrous massive; earthy massive; reniform masses no cleavage omega = 2.90–3.22

epsilon = 2.69–2.94

anisotropic; weakly pleochroic; often shows lamellar twinning hexagonal

ilmenite thick, tabular crystals; compact massive; grains no cleavage; conchoidal fracture n = about 2.7 grayish white; anisotropic hexagonal

lepidocrocite flattened scales; isolated rounded crystals; massive one perfect cleavage, one less so alpha = 1.94

beta = 2.20

gamma = 2.51

gray-white; strongly anisotropic and pleochroic orthorhombic

litharge crusts; alteration product on massicot one cleavage omega = 2.665

epsilon = 2.535 tetragonal

magnetite octahedral crystals; granular massive n = 2.42

brownish gray; isotropic isometric

manganite prismatic crystals, often in bundles; fibrous massive one very perfect cleavage, two less so alpha = 2.25

beta = 2.25

gamma = 2.53

brownish gray-white; anisotropic; weakly pleochroic monoclinic

massicot earthy or scaly massive two cleavages alpha = 2.51

beta = 2.61

gamma = 2.71 orthorhombic

periclase irregular, rounded grains; octahedral crystals one perfect cleavage n = 1.730–1.746 isometric

perovskite (often containing rare earths) cubic crystals uneven to subconchoidal fracture n = 2.30–2.38

dark bluish gray orthorhombic

psilomelane massive; crusts; stalactites; earthy masses orthorhombic

pyrochlore octahedral crystals; irregular masses subconchoidal to uneven fracture n = 1.93–2.02 isometric

pyrolusite columnar or fibrous massive; coatings and concretions one perfect cleavage cream-white; distinctly anisotropic; very weakly pleochroic tetragonal

rutile slender to capillary prismatic crystals; granular massive; as inclusions, often oriented one distinct cleavage omega = 2.556–2.651

epsilon = 2.829–2.895 tetragonal

spinel octahedral crystals; round or embedded grains; granular to compact massive n = 1.715–1.725 isometric

tenorite thin aggregates or laths; curved plates or scales; earthy masses conchoidal fracture light gray-white; strongly anisotropic; pleochroic monoclinic

thorianite rounded cubic crystals uneven to subconchoidal fracture n = about 2.2 (variable) isotropic isometric

uraninite crystals; massive; dendritic aggregates of crystals uneven to conchoidal fracture light brownish gray; isotropic isometric