Online Encyclopedia

Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.

ECLOGITE (from Gr. EKXoyi, a selection)

Online Encyclopedia
Originally appearing in Volume V08, Page 896 of the 1911 Encyclopedia Britannica.
Spread the word: del.icio.us del.icio.us it!

See also:

ECLOGITE (from Gr. EKXoyi, a selection)  , in See also:petrology, a typical member of a small See also:group of metamorphic rocks of See also:special See also:interest on See also:account of the variety of minerals they contain and their microscopic structures and See also:geological relationships . Typically they consist of See also:pale See also:green or nearly colourless See also:augite (omphacite), green See also:hornblende and See also:pink See also:garnet . See also:Quartz also is usually See also:present in these rocks,. but See also:felspar is rare . The augite is mostly a variety of See also:diopside and is only occasionally idiomorphic . The garnet sometimes forms See also:good dodecahedra, but may occur as rounded grains, and encloses quartz, See also:rutile, kyanite, and other minerals very frequently . The hornblende is usually pale green and feebly dichroic, but, in some eclogites which are allied to garnet-amphibolites, it is of dark See also:brown See also:colour . Among the commoner See also:accessory minerals are kyanite (of See also:blue or greyish-blue tints), rutile, See also:biotite, See also:epidote and See also:zoisite, See also:sphene, See also:iron oxides, and B.C . 2000; obi . =23° 55.5' A.D . 1700; obi . =23° 1500 „ =23 52.3 1750 =23 1000 „ =23 48.9 1800 „ =23, 500 „ =23 .45.4 185o „ =23 0 „ =23 41.7 1900 „ =23 A.D . 500 „ =23 38.0 1950 „ =23 1000 „ =23 34.1 2000 „ =23 1500 „ =23 30.3 2050 „ =23 2000 „ =23 26.4 2100 „ =23 2500 =23 22.5 See also:pyrites .

The rutile is invariably in small brown prisms; the kyanite forms bladed crystals, with perfect cleavage; felspar, if present, belongs to basic varieties See also:

rich in See also:lime . Other minerals which have been found in eclogites are See also:bronzite, See also:olivine and glaucophane . The last mentioned is a See also:bright blue variety of hornblende with striking pleochroism . The eclogites in their chemical See also:composition show See also:close See also:affinities to gabbros; they often exhibit relationships in the See also:field which 'show that they were primarily intrusive rocks of igneous origin, and occasionally See also:con-tact alteration can be traced in the adjacent See also:schists . Examples are known in See also:Saxony, See also:Bavaria, See also:Carinthia, See also:Austria, See also:Norway . A few eclogites also occur in the See also:north-See also:west See also:highlands of See also:Scotland . Glaucophane-eclogites have been met with in See also:Italy and the Pennine See also:Alps . Specimens of See also:rock allied to See also:eclogite have been found in the diamantiferous See also:peridotite breccias of See also:South See also:Africa (the so-called " blue ground "), and this has given rise to the theory that these are the See also:parent masses from which the See also:Kimberley diamonds have come . (J . S .

End of Article: ECLOGITE (from Gr. EKXoyi, a selection)
[back]
ECLIPTIC
[next]
ECLOGUE

Additional information and Comments

There are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click and select "copy." Paste it into a website, email, or other HTML document.