Augite Polished Tumble Stones
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.