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EPIDOSITE

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Originally appearing in Volume V09, Page 689 of the 1911 Encyclopedia Britannica.
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EPIDOSITE , in See also:

petrology, a typical member of a See also:family of metamorphic rocks composed mainly of See also:epidote and See also:quartz. In See also:colour they are See also:pale yellow or greenish yellow, and they are hard and somewhat brittle. They may occur in more than one way and are derived from several kinds of See also:rock. Some have been epidotic grits and sandstones; others are limestones which have undergone contact-alteration; probably the See also:majority, however, are allied to See also:epidiorite and See also:amphibolite, and are See also:local modifications of rocks which were primarily basic intrusions or lavas. The sedimentary epidosites occur with See also:mica-See also:schists, sheared grits and granulitic gneisses; they often show, on See also:minute examination, the remains of clastic structures. The epidosites derived from limestones may contain a See also:great variety of minerals such as See also:calcite, See also:augite, See also:garnet, See also:scapolite, &c., but their source may usually be inferred from their See also:close association with See also:talc-silicate rocks in the See also:field. The third See also:group of epidosites may See also:form bands, See also:veins, or irregular streaks and nodules in masses of epidiorite and See also:hornblende-schist. In microscopic See also:section they are often merely a granular See also:mosaic of quartz and epidote with some See also:iron oxides and See also:chlorite, but in other cases they retain much of the structure of the originar rock though there has been a See also:complete replacement of the former minerals by new ones. Epidosites when streaked and variegated have been cut and polished as ornamental stones. They are translucent and hard, and hence serve for See also:brooch stones, and the simpler kinds of See also:jewelry. These rocks occasionally carry See also:gold in visible yellow specks. (J.

S.

End of Article: EPIDOSITE

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