nephelinite

nephelinite

[nef-uh-luh-nahyt]
noun Petrography.
a fine-grained, dark rock of volcanic origin, essentially a basalt containing nepheline but no feldspar and little or no olivine.

Origin:
1860–65; nepheline + -ite1

nephelinitic [nef-uh-luh-nit-ik] , adjective
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World English Dictionary
nephelinite (ˈnɛfɪlɪˌnaɪt)
 
n
a fine-grained basic laval rock consisting of pyroxene and nepheline

Collins English Dictionary - Complete & Unabridged 10th Edition
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Encyclopedia Britannica
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nephelinite

silica-poor (mafic) lava that contains nepheline and pyroxene and is usually completely crystallized. Despite its wide geographic distribution and occasional extensive local development, it is a very rare rock. Known only from Tertiary strata (about 2,500,000 to 65,000,000 years in age), nephelinites are abundant in the Canary Islands, the Azores, the Cape Verde Islands, and Isla Fernando de Noronha off the coast of Brazil. The pyroxene in nephelinites may be either titanium-rich augite or aegirine; plagioclase, if present, is commonly labradorite. Varieties rich in leucite and hauynite are well known. Biotite is characteristic in some types; amphibole is scarce. Accessory minerals may include sanidine, melilite, sodalite, perovskite, apatite, and chromite.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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