Peridotire is the least siliceous of all the igneous rocks, with less than 46 per cent silica by weight, and contains almost no feldspar. So it is a very dark coloured rock, with small pale green crystals of olivine set in a mass of dark pyroxene and hornblende. There are actually several varieties of peridotite. Besides olivine, lherzolite contains both clinopyroxene (augite) and orthopyroxene (ensrarite), wehrlite contains only clinopyroxene; harzburgite contains only orthopyroxene.