GREENSTONE
Greenstone is one of several greenish-colored
metamorphic rocks. It is typically composed of epidote, chlorite, and
plagioclase feldspar. Greenstones are supposed to have a crystalline
texture, but some are weakly foliated (but not enough to be called schist).
Greenstones are the result of low-grade to intermediate-grade metamorphism of
basalts or gabbros. They are relatively common rocks in greenstone belts
in Precambrian shield areas. Many greenstones still preserve physical
aspects of the original basalt lavas (for example, vesiculation or pillow lava
geometry). Some greenstones have been interpreted to be metamorphosed
graywackes (dirty sandstones rich in mafic minerals).
Greenstone (9.0 cm across)
Greenstone