amygdule

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amygdule

[ə′mig‚dyül]
(geology)
A mineral filling formed in vesicles (cavities) of lava flows; it may be chalcedony, opal, calcite, chlorite, or prehnite.
An agate pebble.
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The presence of gonnardite in amygdules is problematic, however, a limited substitution of Ca for Na in natrolite was registered.
However, its position in the succession of other amygdule minerals is uncertain.
Near the top of this unit is a zone of brecciated scoria, slag-like basalt containing numerous amygdules, all less than 2.5 cm in diameter.
It contains numerous small pipe amygdules lined or totally filled with albite and calcite.
Prehnite pseudomorphs after glauberite are widespread within the diapiric amygdules of the first and second flows.
The amygdules are generally filled with white minerals, and give the dark, brownish gray rock a spotted appearance.
Sabina (1992) lists it as "garronite (Na)." The mineral was found as a transparent, yellow to orange crystalline filling in amygdules 2-5 mm across, in a dark sill rock with a spotted appearance (A.
Voggite occurs in cavities within amygdules 1-3 mm across, as matted nests and irregular aggregates of vitreous, colorless to white, acicular capillary crystals rarely exceeding 1 mm in length and 6-8 [micro]m in diameter.
It also occurs as shiny black 10-cm amygdules. More rarely, isolated flat fibers of graphite several millimeters long have been reported.
The mineralogy of the Caledonia mine is typical of the area mines and consists of quartz, calcite, epidote and red K-feldspar that fill amygdules and cement rock fragments.