Prehnite


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prehnite

[′prā‚nīt]
(mineralogy)
Ca2 Al2Si3O10(OH)2 A light-green to white mineral sorosilicate crystallizing in the orthorhombic system and generally found in reniform and stalactitic aggregates with crystalline surface; it has a vitreous luster, hardness is 6-6.5 on Mohs scale, and specific gravity is 2.8-2.9.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Prehnite

 

(named after the Dutch colonel Prehn, who discovered the mineral on the Cape of Good Hope), a sorosilicate mineral that has the chemical composition Ca2 Al[AlSi3O10]·(OH)2 with a trace of Fe replacing the Al. Prehnite crystallizes in the rhombic system. Clearly formed crystals usually have a prismatic, tabular habit and are rare. Prehnite is mainly found as nodular aggregates with radial-columnar structures. It is greenish yellow or gray. Its hardness on Mohs’ scale is 6.5 and its density is 2,800–2,950 kg/m3.

Prehnite is an ordinary hydrothermal mineral that occurs in the cavities of basic effusive rocks together with such minerals as zeolites, calcite, and epidote. It also forms in metamorphic rocks, for example, skarns, and during the decomposition of plagioclases in gabbro and diabases.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Colour Gem imitated (ct) 1 Green Emerald 5.35 2 Green Emerald 3.86 3 Blue-green Paraiba tourmaline 1.71 4 Blue-green Paraiba tourmaline 3.36 5 Red Rubellite 4.45 6 Orange Spessartine 4.71 7 Violet Tanzanite 4.49 8 Yellow-green Peridot 8.83 9 Light blue Aquamarine 7.54 10 Light blue Topaz 8.64 11 Orangey pink Morganite 8.21 12 Violet Amethyst 8.66 13 Violet and yellow Ametrine 8.30 14 Red and green Bicoloured tourmaline 8.37 15 Milky green Prehnite 8.48 16 Colourless with Gold-in-quartz 13.79 'golden' inclusions 17 Colourless with Rutilated or 2.29 narrow foil strips tourmalinated quartz 18 Various iridescent Girasol 4.28 Internal features Crown/ In crown and No.
Other secondary minerals are carbonate, sericite, prehnite, titanite, chlorite, and minor epidote and hematite.
La chlorite, la prehnite et la pumpellyite mineralisee de facon eparse presentes, indiquent que les roches ont atteint le stade d'un facies a prehnite-actinolite.
You can match the range to pretty much any outfit choice, from the lime green prehnite, the smoky brown tiger's eyes and the deep blue lapis lazuli.
These mineral species described are: Hornblende, Epidote, Piemontite, Chabazite, Prehnite, Pyrite, Chalcopyrite, Clinozoisite, Dravite var Tourmaline, Chlorite, Garnet var Almandine, Sulphur (as free crystals), Calcite, Kaolinite, Hyalite Opal.
Subsequently, albitisation transformed scapolite metagabbro and regionally distributed mafic and granitoid rocks to albitites, dominated by albite, with varying amounts of rutile, carbonate, chlorite, and locally prehnite, pumpellyite, and analcime.
The left label shown here is from the Mineralogical Record Label Archive (from Ron Bentley's collection), and the one on the right (still attached to a prehnite specimen) was recently shown to us by Kelly Nash.
At low temperature (<200[degrees]C), Na-Ca-bearing zeolites, trioctahedral (Ca)-Mg-Fe-bearing smectites, and calcite were stable, whereas at high temperature (>200[degrees]C), these minerals were replaced by chlorite-(Mg-Fe), albite, quartz, and Ca-bearing aluminosilicates, including epidote, wairakite, prehnite, and clinozoisite.
Although not a major producer of collector-quality specimens, it has yielded fine examples of heulandite, stilbite, calcite, chalcedony, datolite and prehnite.
The alteration products are mainly saussurite (i.e., fine-grained aggregate of epidote group minerals, albite, prehnite, sericite, and possibly clays).
The regular octahedrons rest on colorless and smoky quartz and are accompanied by other minerals including prehnite, sphene and adularia.
Beautiful yellow-green, transparent prehnite in spheres, hemispheres and "crests" on matrix of graphite-infused rock, from the Merelani mines, Arusha, Tanzania--see the photos in the recent "Tanzanite Issue" (September-October 2009)--has sold for rather high prices in some quarters during the past three years or so, but excellent toenails and small miniatures of the material could be had for $15 to $45 from The Crystal Circle, LLC (www.crystalcircle.com).