Basalt: Fine-Grained Mafic Rock

Basalts may be entirely fine grained or may show phenocrysts of olivine and/or plagioclase. Basalts also may show vesicular or amygdaloidal textures.

This rock displays a fine-grained, porphyritic texture. The relatively small olivine phenocrysts are more clearly displayed in the close-up photo below. Under a microscope, tiny grains of plagioclase, pyroxene and olivine would be visible.
The dark green color of a few of the olivine phenocrysts is obvious in this photograph. Note that the rock is so fine-grained that other crystals are not visible to the naked eye.
This is a vesicular basalt with many small vesicles.
Other basalt samples appear in the pages explaining the fine-grained, fine-grained porphyritic, and vesicular/amygdaloidal textures.