Pyroxene augite

Ureilites contain a variety of trace accessory phases. Metallic spherules composed of cohenite, metal, and sulfide are included in olivine and pigeonite of a few ureilites, and metal, phosphide, and sulfide are present as interstitial phases in most. The interstitial regions also commonly contain fine-grained silicates, including low-calcium pyroxene, augite and Si-Al-alkali glass. 

Single chains Inosilicates Continuous single chains of tetralieda sharing two corners 1 3 Pyroxene (augite)... 

The crystals are generally euhedral and unaltered. The dolerite also contains two and, in some cases, even three pyroxenes augite, pigeonite, and hypersthene. In addition, all specimens contain opaque minerals (magnetite and ilmenite). Quartz and alkali feldspar are prominent in the rocks of the diorite pegmatite and granophyre zones. 

Fig. 13.45 The concentrations of FeO (total iron) of Ca-rich pyroxenes (augite) increase up-section in the Dufek Massif from 12.2% to 16.2% and in the Forrestal Range from 19.9% to 25.3%. The concentration of MgO (not shown) in the same stratigraphic interval decreases up-section from 15.4% to 12.8% (Dufek Massif) and from 11.5% to 8.4% (Forrestal Range). The Ca-poor pyroxenes (pigeonite inverted to Fe-rich hypersthene) have higher concentrations of FeO and MgO than the Ca-rich pyroxenes, but they vary similarly up-section in the Dufek Massif from 21.7% to 25.4% (FeO) and from 20.0% to 16.4% (MgO). The data for the Forrestal Range are incomplete. The stratigraphic variations of FeO and MgO in the pyroxenes of the Dufek intrusion are unambiguous evidence of the evolution of the Dufek magma by fractional crystallization (Data from Himmelberg and Ford 1976)...

The first extensive study of iron-silicate minerals published was by deCoster and co-workers (7, 24). Their results are summarized in Table VI. Augite is a pyroxene containing considerable Na and Ca. No iron percentage was given for the olivine studies. The other minerals are included for comparison. The values given here for biotite are averages for their three untreated samples, which have two sites described as distorted octahedra. Heat treatment at 700°C. for one hour resulted in the emergence of a new Fe peak in biotite. 

Table 5.32 Compositions (in weight %) of natural pyroxenes (samples 1-5 from Deer et al., 1983 samples 6 and 7 from Bonatti et al., 1986) (1) enstatite from a pyroxenite (2) ferrosilite from a thermometamorphic iron band (3) hedembergite (4) chromian augite from a gabbroic rock of the Bushveld complex (5) aegirine from a riebeckite-albite granitoid (6) diopside from a mantle peridotite (7) enstatite from a mantle peridotite. ...

Figure 5,25 Phase stability relations for natural pyroxenes in the quadrilateral. (A) Magmatic pyroxenes (not reequilibrated at low 7). (B) Three-phase region for pyroxenes of stratihed complexes and magmatic series. (C) Pyroxenes reequilibrated in subsolidus conditions. = Pbca orthopyroxene V = augite C2lc) A = pigeonite (P2jlc) 0 = olivine. From Huebner (1982). Reprinted with permission of The Mineralogical Society of America.

Ross M. and Huebner J. S. (1975). A pyroxene geothermometer based on composition temperature relationship of naturally occurring orthopyroxene, pigeonite and augite. In International Conference on Geothermometry and Geobarometry, The Pennsylvania State University. 

In augites, Fe2+ occupancies of the M2 sites increase as the pyroxene becomes increasingly subcalcic. Significant replacement of larger Ca2+ by smaller Fe2+ ions leads to slight contraction of the M2 site (table 5.6), which causes the dominant Fe2+ CF bands located near 10,000 cm-1 (wavelength of 1 micron) and 5,000 cm-1 (2 microns) to move to shorter wavelengths (Adams,... 

Troctolite is thus believed to be the major rock-type forming the central peaks of Copernicus. Reflectance spectra of rays emanating from Copernicus contain more calcic-rich pyroxenes indicative of pigeonite-augite assemblages (Pieters etal., 1985). 

Similar relationships are found for other elements like Sc and Cr. In the sand-sized fractions, the REE distribution patterns show a more pronounced negative Eu anomaly and higher La/Lu ratio for the material from Unit N as compared to samples from Unit B. Interpretation of these observations is difficult because the heavy fractions contain as many as 10 different minerals. Pyroxene (mainly augite), amphiboles (mainly hornblende), iron oxides, chromite, ilmenite, rutile, and zircon were identified by using a polarizing microscope and energy-dispersive X-ray analysis. However, the... 

Most of the olivine-orthopyroxene-(augite) ureilites have poikilitic texmres, consisting of large (up to 5 mm) oikocrysts of low-calcium pyroxene (either orthopyroxene or inverted... 

Figure 31 Lunar meteorite North West Africa (NWA) 773 consists of two distinct lithologies cumulate olivine norite and regolith breccia. The cumulate portion is composed of olivine, pigeonite, augite, feldspar, and opaques (troilite, chromite, Fe-metal). The breccia portion contains fragments of cumulate portion as well as silica glass, hedenbergitic pyroxene, volcanic rocks, and unusual lithic clasts with fayalite + Ba-rich K-feldspar + silica + plagioclase (photograph courtesy of M. Killgore).

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