aegirine Pyroxene mineral, NaFe3+Si2O6; sp. gr. 3.5; hardness 6; monoclinic; greenish-black or brown; occurs as fairly short, prismatic crystals in igneous and metamorphic rocks. A variety intermediate in composition between aegirine and augite is called ‘aegirine—augite’. See also AUGITE; and CLINOPYROXENE.
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Titanite , sphene (titanite) A nesosilicate CaTiSiO4 (O,OH,F); sp. gr. 3.45–3.55; hardness 5; crystals wedge-shaped, occasionally massive; brown, grey, reddish… Biotite , biotite biotite An important rock-forming silicate mineral; a member of the mica group K2(Mg,Fe)6[Si3AlO10]2(OH,F)4, in which the Mg/Fe ratio is less… 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… diabase , dolerite (diabase, microgabbro) A dark-coloured, medium-grained igneous rock which contains plagioclase feldspar of labradorite composition and pyrox… Corundum , corundum Mineral, Al2O3; sp. gr. 3.9–4.1; hardness 9; trigonal; the two main varieties blue and green, but can be yellow, or brown to almost black, a… Rutile , rutile rutile An accessory mineral, TiO2; iron, niobium, and tantalum may also be present; sp. gr. 4.2–5.6; hardness 6.0–6.5; tetragonal; normally re…
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