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.
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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.
Aquamarine specimens have since been collected from miarolitic cavities dug on Anibib 136, Bergsig 167, Davib West 62, Erongorus 166 and Tubussis 22.
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.
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.
A still younger generation of lepidolite that crystallized in small miarolitic cavities is characterized by high concentrations of Li, F, and Rb.
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.
A characteristic of the mineral assemblage, which is similar to that in miarolitic cavities, is an abundance of closely associated astrophyllite, lavenite, rinkite and lorenzenite.
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.