Hedenbergite
| Hedenbergite | |
|---|---|
Hedenbergite
|
|
| General | |
| Category | Pyroxenes |
|
Formula (repeating unit) |
CaFeSi2O6 |
| Strunz classification | 9.DA.15 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/c |
| Identification | |
| Formula mass | 248.09 g/mol |
| Color | brownish green, black |
| Crystal habit | massive, prismatic crystals |
| Cleavage | Good on {110} |
| Fracture | Irregular |
| Tenacity | Brittle |
| Mohs scale hardness | 5.5 - 6.5 |
| Luster | Vitreous, dull |
| Streak | white, gray |
| Diaphaneity | Transparent-Opaque |
| Density | 3.56 g/cm3 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.699 - 1.739 nβ = 1.705 - 1.745 nγ = 1.728 - 1.757 |
| Birefringence | δ = 0.029 |
| Pleochroism | Weak |
| Dispersion | r > v strong |
| References | |
Hedenbergite, CaFeSi2O6, is the iron rich end member of the pyroxene group having a monoclinic crystal system. The mineral is extremely rarely found as a pure substance, and usually has to be synthesized in a lab. It was named in 1819 after M.A. Ludwig Hedenberg, who was the first to define hedenbergite as a mineral. Contact metamorphic rocks high in iron are the primary geologic setting for hedenbergite. This mineral is unique because it can be found in chondrites and skarns (calc–silicate metamorphic rocks). Since it is a member of the pyroxene family, there is a great deal of interest in its importance to general geologic processes.
Hedenbergite has a number of specific properties. Its hardness is usually between five and six with two cleavage plains and conchoidal fracture. Color varies between black, greenish black, and dark brown with a resinous luster. Hedenbergite is a part of a pyroxene solid solution chain consisting of diopside and augite, and is the iron rich end member. One of the best indicators that you have located hedenbergite is the radiating prisms with a monoclinic crystal system. Hedenbergite is found primarily in metamorphic rocks.
The pyroxene quadrilateral easily records the compositions of different pyroxene's contained in igneous rocks, such as diopside, hedenbergite, enstatite, ferrosilite. Hedenbergite is almost never found isolated. From the chemical formulas above, we can tell that the main differences in the compositions will be in terms of calcium, magnesium, and iron. D. H. Lindsley and J. L. Munoz (1969) did such an experiment in order to figure out exactly which combinations of temperature and pressure will cause particular minerals to combine. According to their experiment, at 1000 degrees with a pressure less than two kilobars the stable composition is a mixture of hedenbergite, olivine, and quartz. When the pressure moves to twenty kilobars, the composition moves towards the clinopyroxenes, which contains trace amounts of hedenbergite if any. For temperatures of 750 degrees Celsius, the compositions move from hedenbergite with olivine and quartz to ferrosilite with a greater amount of hedenbergite. If you combine the results of both of these sets of data, you can see that the stability of hedenbergite is more dependent on temperature as opposed to pressure.
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Wikipedia