Plagioclase
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Plagioclase is a series of tectosilicate minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solut
A photomicrograph of a plagioclase crystal (gray) under cross polarized light. The plagioclase crystal shows a distinct banding effect called polysynthetic twinning.
Plagioclase displaying cleavage (unknown scale)
In volcanic rocks, fine-grained plagioclase can display a "microlitic" texture of many small crystals.
Labradorite displaying typical iridescent effect termed labradorescence (unknown scale)
Mafic
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Mafic is a term used in geology to describe silicate minerals, magmas, and igneous rocks that are rich in magnesium and iron, while being relatively low in silica content. Most mafic minerals are dark
Basalt
Apatite
An ʻaʻā flow from Mauna Loa (a volcano in Hawaii), composed of mafic magma.