Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to the fast cooling of lava at the surface of a moon or planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey. By definition, basalt is defined as an aphanitic igneous rock that contains, by volume, less than 20% quartz and less than 10% feldspathoid and where at least 65% of the feldspar is in the form of plagioclase.
On Earth, most basalt magmas have formed by decompression melting of the mantle. Basalt commonly erupts on Io, and has also formed on Earth’s Moon, Mars, Venus, and even on the asteroid Vesta.
Etymology- The word “Basalt” is derived from Late Latin basaltes, misspelling of L. basanites “very hard stone,” which was imported from Ancient Greek basani’ty*s (basanites), from ba’sano*s (basanos, “touchstone”) and originated in Egyptian bauhun “slate”.
Basalt has high liquidus and solidus temperatures—values at the Earth’s surface are near or above 1200 °C (liquidus) and near or below 1000 °C (solidus); these values are higher than those of other common igneous rocks. The majority of basalts are formed at approximately 50–100 km depth within the mantle.
Basalt makes an incredible stone for driveways because of its compressive strength. It is more uniform in color than porphiry and less expensive.
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