Amygdules or amygdales form when the gas bubbles or vesicles in volcanic lava (or other extrusive igneous rocks) are infilled with a secondary mineral such as calcite, quartz, chlorite or one of the zeolites. Amygdules usually form after the rock has been emplaced, and are often associated with low-temperature alteration. Amygdules may often be co...
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secondary deposit of minerals found in a rounded, elongated, or almond-shaped cavity in igneous rock. The cavities (vesicles) were created by the ... [1 related articles]
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http://www.britannica.com/eb/a-z/a/66
A small, bubble-like mass formed from volcanic igneous rock that solidified and a bubble of gas got trapped in the interior.
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http://www.encyclo.co.uk/local/22291
Amygdule refers to a mineral-containing cavity in an igneous rock formed by escaping gas. An unfilled cavity is known as a scoria.
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A gas cavity (vesicle ) in volcanic rock that has been filled with mineral matter such as calcite, chalcedony, or quartz.
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https://www.encyclo.co.uk/local/22327
one of the mineral nodules in an amygdaloid.
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https://www.infoplease.com/dictionary/amygdule
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