Augite
Augite is a common rock-forming mineral classified within the pyroxene group, specifically in the clinopyroxene subgroup. Here are detailed aspects concerning this mineral:
Physical Properties
- Chemical Formula: (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6
- Color: Typically black, dark green, or brown
- Luster: Vitreous to dull
- Hardness: 5.5 to 6 on the Mohs scale
- Cleavage: Two directions, intersecting at approximately 87 and 93 degrees
- Crystal System: Monoclinic
- Streak: Colorless or light grey
- Density: 3.2 to 3.6 g/cm³
Occurrence
Augite is commonly found in igneous rocks such as:
It can also occur in metamorphic rocks where it forms through the recrystallization of precursor minerals during metamorphism.
History and Etymology
The name Augite comes from the Greek word "auge", meaning brightness or shining, which refers to the mineral's often lustrous appearance. This mineral has been recognized and described since the early 19th century by mineralogists interested in igneous rock compositions.
Use and Significance
While Augite is not commonly used as a gemstone due to its dark color and lack of transparency, it plays a significant role in:
- Geology: It's a key indicator mineral in identifying rock types and understanding the formation conditions of igneous rocks.
- Mineralogy: Augite's composition provides insights into the geochemical processes and the cooling history of magma.
Identification
Augite can be identified by its:
- Distinctive two-directional cleavage
- Color and streak
- Hardness
- The presence of a characteristic "hourglass" extinction under the polarizing microscope due to its zoning
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