Tephrite

tephrite [′te‚frīt]

(petrology)

A group of basaltic extrusive rocks composed chiefly of calcic plagioclase, augite, and nepheline or leucite, with some sodic sanidine.

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Tephrite 

a porphyritic volcanic rock of ashgray, dark gray, or, rarely, black color.

The principal mass in tephrite is fine-grained, semivitreous, and dense and contains inclusions of pyroxene (titanaugite, acmite-augite, and sometimes aegirihe) and plagioclase. It sometimes contains anorthoclase, sanidine, and leucite and, less frequently, haiiyne, nepheline, hornblende, biotite, and titanite. Leucite, nepheline, sodalite, or other tephrites are distinguished according to the predominant feldspathoids. Like other effusive rocks, tephrite is accompanied by ashes, lapilli, and tuffs.

Tephrites are the effusive analogues of plutonic alkaline tetralite gabbroids. They are part of magma formations, which counts for the concentration of titanium, tantalum, zirconium, nepheline, and rare and trace elements. Leucite tephrites are found among the lavas of Vesuvius and Monte Somma in Italy; nepheline tephrites are found in the Eifel region of the Federal Republic of Germany and in the Azores and Canary Islands; sodalite, haiiyne, and analcime tephrites are found in Czechoslovakia and central France.