Basalt porphyry |
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Basalt porphyryExtrusive igneous rock of ultramafic composition.This is a cinder block from a classic locality, a cinder cone near the Green Sand Beach on the Big Island of Hawaii. The green crystals of olivine (peridot) are phenocrysts imbedded in a dark vesicular basalt lava. The peridot crystals weathering from the basalt are the origin of the green sand on the beach. |
| https://gotbooks.miracosta.edu/rocks/igneous/35.html | 2/2/2021 |