What is "basanite"

Basanite \Bas"a*nite\, n. [L. basanites lapis, Gr. ba`sanos the touchstone: cf. F. basanite.] (Min.) Lydian stone, or black jasper, a variety of siliceous or flinty slate, of a grayish or bluish black color. It is employed to test the purity of gold, the amount of alloy being indicated by the color left on the stone when rubbed by the metal. [1913 Webster] ||

n. (context geology English) A basaltic extrusive rock, similar to chert

Basanite is an igneous, volcanic ( extrusive) rock with aphanitic to porphyritic texture.

The mineral assembly is usually abundant feldspathoids ( nepheline or leucite), plagioclase, and augite, together with olivine and lesser iron-titanium oxides such as ilmenite and magnetite- ulvospinel; minor alkali feldspar may be present, as illustrated by the position of the field for basanite in the QAPF diagram. Clinopyroxene ( augite) and olivine are common as phenocrysts and in the matrix. The augite contains significantly greater titanium, aluminium and sodium than that in typical tholeiitic basalt. Quartz is absent, as are orthopyroxene and pigeonite. Chemically, basanites are low in silica (42 to 45% SiO) and high in alkalis (3 to 5.5% NaO and KO) compared to basalt, which typically contains more SiO, as evident on the diagram used for TAS classification. Nephelinite is yet richer in NaO plus KO compared to SiO.

Basanites occur both on continents and on ocean islands. For example, together with basalts, they are produced by hotspot volcanism in the Hawaiian and the Comoros Islands.