Description: Augite is an important rock-forming
mineral in many igneous rocks, especially in gabbros
and basalts, and is also found in some hydrothermal
metamorphic rocks. Augite is a part of an important
solid solution series of the pyroxene group. The series
includes the minerals hedenbergite , CaFeSi2 O6, and
diopside , CaMgSi2 O6. A series occurs when ions (in
this case iron and magnesium) can freely substitute
between each other. Augite is the intermediate member
of the series. However, augite is not just an intermediate,
but is unique in that it contains percentages of sodium
and aluminum that are mostly lacking in diopside and
hedenbergite. The magnesium content is also larger in
augite than in either of the other two minerals. The
diopside-hedenbergite series is analogous to amphibole's
tremolite - actinolite series.
Mineral specimens of augite, while ordinarily unattractive
and not very interesting, can have some specimens that
are very striking in appearance and are of interest
to many mineral collectors. Its name is derived from
the greek word augites which means "brightness"
in allusion to its relatively high luster that is seen
on some exceptional specimens.