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A blastoporphyritic, or sometimes porphyroblastic, metamorphic rock of igneous origin.
A feldspathic metasedimentary rock having the appearance of a porphyry.
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 It might be outdated or ideologically biased.



(also porphyritoid), a rock formed as a result of the metamorphism of rocks with similar composition, such as diabases, porphyrites, or gangues. Porphyroid is usually composed of feldspar, amphibole, pyroxene relicts, calcite, chlorite, talc, and clay; sometimes it contains quartz and zoisite. As a result of strong cataclasis, porphyroid sometimes takes on a slaty texture.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
A thin section of sample ODB-1488_65 of diopside-tremolite shows the presence of elements of reticulate, porphyroid, streaky texture (Gorbatsevich et al., 2011).
Sample ODB-2155_15 has a porphyroid texture and is composed of microcline-perthite large crystals, fine grains of plagioclase and quartz (Gorbatsevich et al., 2011).
Various types of amphibolites and metagabbros are the most common and in places they contain streaks of gneisses and acid metavolcanics (porphyroids).