Augite is a member of the pyroxene group of simple silicates, in which the SiO 4 tetrahedra are linked by sharing two of their four corners to form continuous chains. For this reason they are often referred to as single chain silicates.
Pyroxenes are subdivided into those with orthorhombic symmetry (orthopyroxenes), and those with monoclinic symmetry (clinopyroxenes), with augite being the most common of the clinopyroxenes.
Augite is commonly found in igneous rocks such as gabbros, basalts and andesites, and high grade metamorphic rocks (granulites).
Chemical composition - (Ca, Na)(Mg, Fe, Al)(Al, Si) 2 O 6
Hardness - 5-6
Specific gravity - 3.2-3.6
Transparency - Transparent to mostly translucent or opaque
Colour - Dark green, brown and black
Streak - Greenish white
Lustre - Vitreous
Cleavage/fracture - Imperfect in two lengthwise directions at close to right angles / uneven
Crystal habit/mode of occurrence - Prismatic (distinctive square cross section), tabular / granular
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