tetrahedrite An end-member of the tetrahedrite series from tetrahedrite (Cu,Fe)12Sb4S13 to tennantite (Cu,Fe)12As4S13; if sliver is present in quantity (up to 30%) the mineral is called freibergite; sp. gr. 4.5–5.1; hardness 3.0–4.5; hardness 4.0; greyish-black; metallic lustre; black streak; normally massive but tetrahedral when crystalline; occurs in hydrothermal veins in association with other copper and iron sulphides.
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wolframite , wolframite Ore mineral for tungsten, with the formula (Fe,Mn)WO4; sp. gr. 7.0–7.5; hardness 5.0–5.5; monoclinic; grey-black to brownish-black; browni… Uraninite , uraninite (pitchblende) Mineral, UO2; sp. gr. from 8.5 when massive to 10 for unaltered crystals; hardness 5–6; cubic; it is brownish-black or grey-b… ilmenite , ilmenite Mineral, FeTiO3; sp. gr. 4.5–5.0; hardness 5–6; trigonal; black; black to brownish-red streak; sub-metallic lustre; crystals normally thick… chromite , chromite Member of the chromite group of minerals in the spinel group, Fe2+Cr2O4, along with magnesiochromite (MgCr2O4); sp. gr. 5.1; black; sub-meta… Magnetite , magnetite (loadstone, lodestone) An important rock-forming iron oxide Fe2+Fe3+2O4 (FeO.Fe2O3) and member of the spinel group of minerals; belongs to… pentlandite , pentlandite An iron and nickel sulphide, with the formula (FeNi)9S8, and the main ore mineral for nickel; sp. gr. 4.5–5.0; hardness 3–4; cubic; light…
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