Said of crystalline rocks which contain a relatively low percentage of silica, as basalt.
A descriptive term for igneous rocks containing less than about 52 percent silica (SiO2).
Crystalline rocks (igneous and metamorphic) can be classified on their chemical composition, as reflected in the amount of SiO2 present (so-called normative composition). Rocks with rather low SiO2 contents (without free silica - the mineral quartz) are termed "basic". They will generally also contain lots of dark minerals (e.g. amphiboles or pyroxenes, perhaps olivine). Examples include the igneous rocks basalt and gabbro.
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It describes to an igneous rock which has a relatively low silica content, between 45-52% SiO2. They are relatively rich in iron, magnesium and calcium and is thus included in most mafic rocks.
A descriptive term applied to igneous rocks (basalt and gabbro) with silica (SiO2) between 44% and 52%.
An igneous rock relatively poor in silica, such as basalt.
basic rock, plutonic or volcanic rock having a silica content (SiO2) comprised between 45% and 52 %.