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Encyclopedia > Prehnite
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Prehnite is a phyllosilicate of calcium and aluminium with the formula: Ca2Al(AlSi3O10)(OH)2. Limited Fe3+ substitutes for aluminium in the structure. Prehnite crystallizes in the orthorhombic crystal system. It is brittle with an uneven fracture and a vitreous to pearly lustre. Its hardness is 6-6.5, its specific gravity is 2.80-2.90 and its color varies from light green to grey or white. It is translucent. The silicate minerals make up the the largest and most important class of rock-forming minerals. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ... Jump to: navigation, search General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... In crystallography, the orthorhombic crystal system is one of the 7 lattice point groups. ... Quartz crystal A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... Relative density (also known as specific gravity) is a measure of the density of a material. ...


Though not a zeolite, it is found associated with them and with datolite, calcite, etc. in veins and cavities of basaltic rocks, sometimes in granites, syenites, or gneisses. It was first discovered in South Africa by Colonel Prehn, an early Dutch governor of the Cape of Good Hope colony. Zeolite Zeolites (Greek, zein,to boil;lithos,a stone) are minerals that have a porous structure. ... A borosilicate of lime commonly occuring in glassy, greenish crystals. ... Calcite from Brushy Creek Mine, Missouri, USA. The mineral calcite is a calcium carbonate corresponding to the formula CaCO3 and is one of the most widely distributed minerals on the Earths surface. ... Basalt Basalt is an extrusive igneous rock, sometimes porphyritic, and is often both fine-grained and dense. ... Quarrying granite for the Mormon Temple, Utah Territory. ... Syenite Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts. ... Banded gneiss with dike of granite orthogneiss Gneiss is a common and widely distributed type of rock formed by high grade regional metamorphic processes from preexisting formations that were originally either igneous or sedimentary rocks. ... Jump to: navigation, search 1888 Map of the Cape of Good Hope The Cape of Good Hope is a headland in South Africa, near Cape Town, traditionally— and incorrectly — regarded as marking the turning point between the Atlantic Ocean and the Indian Ocean (Technically, the division between the two oceans...


Reference

  • Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0471805807

See also


  Results from FactBites:
 
Prehnite - LoveToKnow 1911 (315 words)
Prehnite is sometimes classed with the zeolites, since it occurs under the same conditions as these minerals and often in association with them: the small amount of water (4-4%) is, however, expelled only at a red heat and is therefore not water of crystallization.
Prehnite occurs as a mineral of secondary origin in the amygdaloidal cavities of basic igneous rocks, such as basalt and diabase, and less often, in veins in granite and gneiss.
Prehnite is sometimes cut and polished for small ornaments; it then somewhat resembles chrysoprase in appearance.
Prehnite (496 words)
Prehnite is found in faintly yellowish-white coarse lamellar to platy aggregates, some of the plates being in fan-shaped groups.
The early analyses gave quite unsatisfactory ratios for prehnite until it was discovered that the mineral was mixed with pectolite, but after correction for the presence of enough of that mineral to account for the alkalies found, both gave fairly satisfactory ratios.
After it was learned that pectolite is fluorescent under the iron-arc spark, whereas prehnite is not, some of the material from which analysis 2 was made was again separated, first in a heavy solution and finally under the spark, and thus a sample almost free from pectolite was obtained.
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