Basalt | A soil type  defined by John Szabo (2016, p.248) as ‘an igneous rock that forms both intrusively, but mostly extrusively, from lava rich in iron and magnesium, and poor in potassium and sodium, with less that 50 per cent silica (mafic). Basalt’s low viscosity leads to more gentle eruptions. Oceanic crust is composed primarily of basalts (or closely related gabbro and peridotite) formed at mid-ocean rift zones, making it the most abundant rock type on the earth’s surface, even if it makes up only a few per cent of the continental surface.’

Bibliography

John Szabo (MS), Volcanic Wines, (Jacqui Small, 2016).