Feldspar - Encyclopedia.com
网页2018年5月29日 · feldspar Group of common rock-forming minerals that all contain aluminium, silicon and oxygen, but with varying proportions of potassium, sodium and calcium. They are essential constituents of igneous rocks. Hardness 6–6.5; r.d. 2.5–2.8. Feldspar Feldspar is the most common mineral on Earth [1], constituting approximately …
Feldspars - Encyclopedia.com
网页2018年5月8日 · feldspars. feldspars The most important group of rock-forming silicate minerals, including the alkali feldspars KAlSi 3 O 8 to NaAlSi 3 O 8 (K-feldspar to albite) and the plagioclase feldspars NaAlSi 3 O 8 to CaAl 2 Si 2 O 8 ( albite to anorthite). The potassium, sodium, and calcium end-members can be taken to represent the three …
Alkali Feldspar - Encyclopedia.com
网页2018年5月8日 · alkali feldspar A group of silicate minerals that contain the alkali metal elements potassium and sodium. The normal feldspar minerals (including the calcium-bearing varieties) can be plotted on a chemical basis into a triangle which has KAlSi 3 O 8 (potassium feldspar, sanidine, orthoclase (Or), or microcline), NaAlSi 3 O 8 (sodium …
Granite - Encyclopedia.com
网页2018年5月8日 · Granite, which makes up 70 – 80% of Earth's crust, is an igneous rock formed of interlocking crystals of quartz, feldspar, mica, and other minerals in lesser quantities. Large masses of granite are a major ingredient of mountain ranges. Granite is a plutonic rock, meaning that it forms deep underground.
Plagioclases | Encyclopedia.com
网页2018年5月8日 · Plagioclase is a form of the mineral feldspar . All feldspars are crystals of aluminum, oxygen , and silicon , plus a major additive. In the case of plagioclase, the additive is calcium, sodium, or a blend of both. Miscellaneous impurities may also be present. Like other feldspars, plagioclases have a vitreous (glassy) luster, are translucent ...
Porcelain - Encyclopedia.com
网页2018年5月23日 · Feldspar, a mineral comprising mostly aluminum silicate, and flint, a type of hard quartz, function as fluxes in the porcelain body or mixture. Fluxes reduce the temperature at which liquid glass forms during firing to between 1,835 and 2,375 degrees Fahrenheit (1,000 and 1,300 degrees Celsius).
Gneiss - Encyclopedia.com
网页2018年6月8日 · Gneiss (pronounced "nice") is a metamorphic rock consisting mostly of quartz and feldspar and showing distinct layering or banding. The layering of a gneiss may be weak or well-developed and consists of varying concentrations of biotite, garnet, hornblende, mica, and other minerals .
Dacite - Encyclopedia.com
网页2018年5月8日 · dacite. dacite A light-coloured, fine-grained igneous rock containing 63–70 wt.% SiO 2, as well as plagioclase feldspar, alkali feldspar, quartz, biotite, and hornblende as essential minerals, and sphene, apatite, and magnetite as accessory minerals. Plagioclase feldspar dominates over alkali feldspar in a 2:1 ratio.
Andesite - Encyclopedia.com
网页2018年5月14日 · Andesite. Andesite is the most common volcanic rock after basalt . It is porphyritic, that is, consists of coarse crystals (phenocrysts) embedded in a granular or glassy matrix (groundmass). Having a silica content of 57%, it is in the intermediate category (52 – 66% silica) of the silicic – mafic scale. The large volcanic mountain chains ...
albitization | Encyclopedia.com
网页albitization. albitization The partial or complete replacement of pre-existing plagioclase feldspar or alkali feldspar by albite. There are a number of ways in which this can be achieved. A common process involves the residual water-rich vapour released during the final stages of crystallization of a granite body.