- A fine-grained
igneous rock dominated by dark-colored
consisting of plagioclase feldspars (over 50
percent) and ferromagnesian silicates.
Basalts and andesites represent about 98 percent of
all extrusive rocks.
Source: Leet, L. Don. 1982.
Physical Geology, 6th Edition. Englewood Cliffs, NJ: Prentice-Hall
- A general term for dark-colored mafic igneous rocks, commonly extrusive
but locally intrusive (e.g., as dikes), composed chiefly of calcic
plagioclase and clinopyroxene; the fine-grained equivalent of gabbro.
Nepheline, olivine, orthopyroxene, or quartz may be present. Adj.
basaltic. CF: tholeiite
Dictionary of Mining, Mineral, and Related Terms