index mineral


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index mineral

[′in‚deks ‚min·rəl]
(petrology)
A mineral whose first appearance in passing from low to higher grades of metamorphism indicates the outer limit of a zone.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
A succession of five foliation intersection/inflection axes preserved in porphyroblasts (FIAs), sequential growth of metamorphic index minerals, spectacular inclusion trails and in-situ dating of monazite grains within porphyroblasts show that the Balcooma Metamorphic Group has been affected by 5 orogenic cycles of different intensities from ~476+-5 to 408.8+-8.9 Ma.