Common pyroxene (Augite)

Ca(Mg, Fe ²⁺ , Fe ³⁺ , Ti, Al)[(Si,Al) ₂ O ₆ ]

[Chemical composition] The amount of Al-substituted Si in ordinary pyroxene is slightly larger, and most of them exceed 5%. Some people think that Al-generation Si can reach 1/8 to 1/2. In addition, Ti ⁴⁺ and Fe ³⁺ are also present instead of Si.

The minor components of ordinary pyroxene are Ti, Na, Cr, Ni, Mn, and the like. Ti content is generally not high, pyroxene titanium-containing TiO ₂ is usually 3% to 5%, some as high as 8.97%.

[Crystal structure] monoclinic system; Z=4. The unit cell parameters for synthesizing ordinary pyroxene without Al are approximately a ₀ = 0.970 to 0.982 nm, b ₀ = 0.889 to 0.903 nm, c ₀ = 0.524 to 0.525 nm; and β = 105 to 107. Due to the substitution of Al for Si and the presence of six-order coordination Al, the change of unit cell parameters is obviously affected. Generally, a ₀ and b ₀ decrease with the increase of Al, and c ₀ and β increase with the increase of Al. The structural characteristics are summarized in the Huishui family.

Figure G-28 Ordinary pyroxene crystals and twin crystals (cited from Pan Zhaoyu et al., 1993)

(a) single crystal, (b) twin (with {100} as the joint)

Parallel double sided: a{100}, b{010}, c{001}; slanted square column: m{110}

[Form] Short columnar crystal (Fig. G-28). The cross section is a regular octagon. Ordinary pyroxene is also granular. Simple twin and polycrystalline twin crystals formed by (001) and (100) are more common, and sometimes become simple twins according to (101) and (122).

[Physical properties] gray brown, brown, greenish black; streaks are colorless to light brown. The cleavage {110} is completely, with an angle of 87°; with {100}, {010} split. Hardness 5.5 to 6. The relative density is 3.23 to 3.52.

[genesis and occurrence] are common in various basic intrusive rocks, eruptive rocks and tuffs , and good crystals can be seen. Zhangjiakou in northern Hannuoba basalt olivine and pyroxene, plagioclase symbiosis. It is also common in metamorphic rocks and contact metasomatism rocks. Ordinary pyroxene is often etched into minerals such as amphibole, epidote, and chlorite.

[Identification characteristics] Green black, short columnar crystal form and its cleavage are characterized.

[Main use] Only mineralogical and petrological.

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