Description
Augite is a mafic mineral with the chemical formula (Ca,Na)(Mg,Fe,Al)(Al,Si)2O6. It is a solid solution of the pyroxene group with diopside and hedenbergite. The crystals are monoclinic and prismatic. Augite occurs mainly in igneous rocks such as gabbros and basalts, and in metamorphic rocks at hydrothermal vents. Some specimens have a remarkable brilliance, hence the name (Greek: augites means "brightness"), although normally the crystals have a dull (dark green, brown, or black) luster. Augite occurs in the sandy fraction of Dutch Quaternary river sediments. In the heavy mineral analyses of the Netherlands Geological Survey during the second half of the twentieth century, the mineral was classified in the so-called unstable group and was considered a volcanic mineral.[2] In Dutch Rhine sediments, augite is an important mineral and can sometimes constitute more than half of the heavy mineral fraction[3]. The mineral characterizes the sandy sediments of the Urk and Kreftenheye Formations. In especially coarse-grained sand deposits of the Rhine, it became an important constituent during the 'Brockentuff' or 'Selbergittuff' phase of Eifel volcanism. In the Netherlands, an age of 450,000 years is considered for the onset of larger amounts (>c. 3%) of augite in the Urk Formation. The nakhlites, a group of meteorites originating from Mars, are rich in augite.
Augiet
