miarolitic

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miarolitic

[¦mē·ə·rō¦lid·ik]
(petrology)
Of igneous rock, characterized by small irregular cavities into which well-formed crystals of the rock-forming mineral protrude.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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Two generations of albite have been described from the Erongo Mountains' miarolitic cavities (Jahn and Bahmann, 2000): "Albite 1" consists of rare, several-centimeter-long but millimeter-thick acicular crystals.
Beryl is one of the premier collectible minerals from the Erongo miarolitic cavities. Individual crystals typically have a variety of habits, from simple hexagonal prisms with basal pinacoids to complex combinations of pyramidal and pinacoidal faces.
Biotite is a minor constituent in some of the miarolitic cavities (von Bezing, 2006).
The crystals are either collected from weathered granite pegmatites or alluvium, or they are removed from the miarolitic cavities by the local native artisans.
The reddish-gray quartz monzonite contains sparse, small miarolitic cavities lined with quartz (sometimes smoky) and tan to pink microcline with occasional albite, epidote and pale yellow to greenish muscovite.
Miarolitic cavities up to 1 meter x 35 cm x 20 cm contain white to clear quartz, creamy microcline and pale yellowish green muscovite.
The bladed and radiating variety, cleavelandite, occurs within miarolitic cavities with amazonite, smoky quartz, and topaz.
The wall rock around miarolitic cavities often contains numerous small, rounded vesicles 1-3 mm across which provide a substrate for a rich and varied assemblage.
It is likely that the miarolitic cavities were formed by volatiles exsolving from the magma during the final stages of solidification.
Some miarolitic cavities found generally near the erosional surface contain minerals that have been subjected to oxidation and leaching, probably by meteoric water.
These miarolitic cavities commonly contain well crystallized plagioclase and pyroxene, the principal components of the host dolerite.
Simple black prismatic crystals of titaniferous diopsidic augite (Joplin, 1964) reaching 5 mm in length are occasionally observed in the miarolitic cavities associated with the pegmatite schlieren.