orthoclase feldspar
41Lamprophyre — Lamprophyres (Greek λαµπρός (lamprós) = bright and φύρω (phýro) = to mix) are uncommon, small volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks and small intrusions. They are alkaline silica… …
42Nepheline syenite — of the Intrusive Complex of Tanguá, State of Rio de Janeiro, Brasil (Motoki et al., 2011a) Nephelene syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. The rocks are mostly pale colored, grey or… …
43Leucite — is a rock forming mineral composed of potassium and aluminium tectosilicate K [AlSi2O6] . Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster in 1821, they are not optically isotropic, and are therefore… …
44Celsian — is an uncommon feldspar mineral, barium aluminosilicate, BaAl2Si2O8. The mineral occurs in contact metamorphic rocks with significant barium content. Its crystal system is monoclinic, and it is white, yellow, or transparent in appearance. In pure …
45microcline — /muy kreuh kluyn /, n. a mineral of the feldspar group, potassium aluminum silicate, KAlSi3O8, identical in composition with orthoclase but having triclinic instead of monoclinic crystals, used in making porcelain. [1840 50; MICRO + cline < Gk… …
46Granite — For other uses, see Granite (disambiguation). Granite Igneous Rock Granite containing potassium feldspar, plagioclase feldspar, quartz, and biotite and/or amphibole Composi …
47Oligoclase — from Chihuahua, Mexico General Category plagioclase, feldspar, tectosilicate …
48Sunstone — For other uses, see Sunstone (disambiguation). Sunstone General Category Crystal Chemical formula …
49metamorphic rock — Any of a class of rocks that result from the alteration of preexisting rocks in response to changing geological conditions, including variations in temperature, pressure, and mechanical stress. The preexisting rocks may be igneous, sedimentary,… …
50Important gemstones — ▪ Table Important gemstones mineral gem name colour Mohs hardness* specific gravity* beryl aquamarine sky blue to greenish blue 7½–8 2.68–2.71 emerald green 2.68–2.74 goshenite colourless; greenish yellow, yellow green, brownish same as… …
