Tephrite


Also found in: Dictionary, Wikipedia.
Related to Tephrite: phonolite, trachyte

tephrite

[′te‚frīt]
(petrology)
A group of basaltic extrusive rocks composed chiefly of calcic plagioclase, augite, and nepheline or leucite, with some sodic sanidine.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
Mentioned in ?
References in periodicals archive ?
DO-3 DO-4 Locality, Tephrite, Zeolitized rock type Dobranka tephrite, Ovesna Si[O.sub.2] (wt.%) 44.85 46.88 Ti[O.sub.2] 1.78 3.01 [Al.sub.2][O.sub.3] 18.08 15.99 [Fe.sub.2][O.sub.3] 7.71 5.67 FeO 3.23 4.84 MnO n.a.
Hibsch (1915) recognized at least two petro-graphically different sets of lavas in the Dobranka area: (i) the lower set of nepheline to sodalite "teph-rites" with a tendency towards feldspathoidal trachyandesite (e.g., Dobranka locality), and (ii) the upper set of "leucite" tephrites (pseudoleucite).
The unusual abundance of larger vesicles and amygdales in this rock facies is not very common (prevailing in intrusive tephrites) in the Ceske stfedohofi Mts.
From oldest to youngest (Elston and Snider, 1964), they are diabase porphyry, olivine diabase porphyry, fine-grained diabase, latite or trachyte, tephrite porphyry, and rhyolite.
On a total alkali-silica plot (LeMaitre, 1984) compositions span a broad range from tephrite to trachyte (Fig.
Rhyolite has the lowest Th/U ratio (3.1, one analysis) followed by tephrite (3.3, two analyses), latites and trachytes (3.4 to 3.7, three analyses), diabase porphyry (4.3, one analysis), olivine diabase porphyry (4.7, one analysis) and fine-grained diabase (4.2 to 4.8, three analyses).
The Eocene lavas are mostly andesites, trachyandesites, trachybasalts and analcime-bearing tephrites with shoshonitic to alkaline geochemical signatures.
tephrites and foidites) prevailing over the olivine ones.