Epidote


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epidote

[′ep·ə‚dōt]
(mineralogy)
A pistachio-green to blackish-green calcium aluminum sorosilicate mineral that crystallizes in the monoclinic system; the luster is vitreous, hardness is 6½ on Mohs scale, and specific gravity is 3.35-3.45.

Epidote

 

a rock-forming mineral of the silicate class, with chemical composition Ca2[Al, Fe, Mn]3[SiO4][Si2O7]O(OH). Epidote crystallizes in the monoclinic system, often forming well-faceted, elongated prismatic crystals. It also occurs in the form of granular, divergent, or parallel columnar aggregates. It has a perfect cleavage and a vitreous luster. Its hardness on Mohs’ scale is 6–7. Its density increases from 3,300 to 3,450 kg/m3 with increasing iron and manganese content. The color of epidote is related to inclusions of ions of transition metals in the structure and varies from colorless or bluish gray (for clinozoisites, which do not contain Fe and Mn) to dark green (for large concentrations of Fe). Epidote with a high Mn content, called piedmontite, has a pink or red-brown color.

Epidote is a typical mineral of limestone skarns, as well as of low- and medium-temperature metamorphic rocks rich in Ca. Experimental study of certain important chemical reactions between epidote and other silicates (garnet and anorthite) has made it possible to use epidote as an indicator of the physicochemical conditions of the formation of the rocks in which it is found.

REFERENCE

Kepezhinskas, K. B., and V. V. Khlestov. Statisticheskii analiz mine-ralov gruppy epidota i ikhparageneticheskie tipy: Moscow, 1971.

L. IA. ARANOVICH

References in periodicals archive ?
In the ZMT--336 samples that is harvested from Zone Skarn are mineral garnet, plagioclase, epidote along with diopcide in the background of rock in the strip form of diopcide and epidote minerals.
The first one corresponds to epidote-amphibolite facies, represented by hornblende + epidote group minerals + quartz + albite [+ or -] garnet (Figure 3c).
The MPH sample was dominated by diopside and hornblende; RSB by epidote, garnet, and biotite; and SQB by rutile, epidote, staurolite, and apatite.
Flat veins are generally less abundant, thinner (up to 15 cm), and are dominated by silicate minerals (quartz, potassic feldspar, epidote, and axinite) and carbonate.
Athol, for example, is noted for allanite and epidote.
Zircon (colourless to pale gray), tourmaline (brown, greenish brown, yellow and green), epidote (colourless, lemon yellow to the characteristic pistachio green colour), rutile (blood red colour) are the non-opaque accessories and among them tourmaline is the most dominant followed by zircon.
The coarse mineral fraction is overwhelmingly dominated by quartz grains, although there are a number of minor (<5%) mineral components including plagioclase feldspar, epidote, and tourmaline.
Reaction halos of iron-deficient tuff surround the stromatolite layers where iron was locally assimilated by them during epidote formation.
Kyanite, garnet, monazite, and amphibole are common minerals, while apatite, anatase, titanite, corundum, pyroxene, and epidote are rare.
The heavy secondary alteration of prehnites, epidote, and native copper infill the vesicles formed by this process.
These granites are presumed to be part of the peninsular gneissic complex and to contain basic enclaves of aplite, pegmatite, epidote, and quartz veins.
Reactions at such high temperatures (up to 350 [degrees] to 400 [degrees] c) produce a characteristic suite of alteration minerals (chlorite, sodium-rich feldspar, amphibole, epidote, and quartz), which, in turn, controls the fluid composition.