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Metamorphic
Rocks
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Gneiss (pronounced like your relative)
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Gneiss (pronounced like your relative) |
| "Colour:
Grey or pink but with dark streaks and layers. Texture: Medium- to coarse grained. Characterized by discontinuous, altering light and dark layers, the former usually having a coarsely granular texture while the latter, which often contains mica, may be foliated. Structure: In addition to the gneissose texture described above, gneisses tend to be banded on a large scale with layers and streaks of darker and lighter coloured gneiss. Granite and quartz veins and pegmatites are common. May be folded. Mineralogy: Feldspar is abundant and, together with quartz, forms the granular, lighter coloured layers. Muscovite, biotite and hornblende are commonly present, while any of the minerals characteristic of higher grades of regional metamorphism may occur. Field relations: At the highest grades of metamorphism rocks may approach melting temperature when they are able to recrystallize freely and so produce the textures characteristic of gneisses. Thus gneisses occur, in association with migmatites and granites, in the central parts of metamorphic belts." (Hamilton et al 1976, 148) |
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Common
Metamorphic Rocks:
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Rock types:
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