BRAZIL - MG
Governador Valadares is an Augite-Olivine Achondrite, classified as Nakhlite belonging to the SCN clan, which are meteorites from the planet Mars.
The Governador Valadares meteorite exhibits a visibly porphyritic texture. Augite phenocrystals are embedded in a fine-grained interstitial material, consisting of glass and semi-radiant skeletal crystals of plagioclase, K-feldspar, silica, chlorapatite, pigeonite and opaque phases. The mineralogical composition and texture suggest that most or all of the olivine is also an interstitial phase. The entire texture can be properly defined as trachytic-porphyritic with variolitic mesostasis. Augite grains commonly exhibit wide wide twinned bands, have elongated tabular habits. The textural evidence suggests that the rock represents a cumulative that was in the act of flowing during or after the formation of the crystals. A slight evidence of shock metamorphism is indicated by the wavy extinction of the silicate grains. Source: Gomes & Keil (1980).
According to Berkley et al. (1979), the meteorite essentially consists of subhedral to euhedral augite with lesser amounts of anhedral to subhedral interstitial olivine. The augite is weakly zoned, with Fe / Mg slightly growing towards the edges of the grain. The compositional average for pyroxene is En38.9 Fs22.6 Wo38.5. Olivine exhibits a more zoned composition, in some cases varying up to 7.0 mol% of Fa (Fa63 core and Fa70 edge). The composition of the olivine core also varies from grain to grain (Fa68-62) with an average of Fa66.2. Olivine is often found as veins or surrounded by a brownish red alteration product identified as iddingsite. The minor constituents of the meteorite include interstitial pigeonite (composition ranging from En32-21 Fs61-66 Wo7-13; mean En26.7 Fs63.9 Wo9.4), plagioclase (Ab48.3 An48.8 Or2.9) K-feldspar ( Ab31.0 An5.0 Or64.0), titanomagnetite, ilmenite, troilite, chalcopyrite, pyrite, chlorapatite and pure SiO2. Source: Gomes & Keil (1980).
The total chemical data of Governador Valadares agrees with all those listed in the literature for the augond-olivine achondrite meteorites Lafayette and Nakhla, being classified as Nakhlito. The pyroxenic composition of the meteorite is quite apparent, with hyperstene and diopside composing up to 72% of the rock and the rest including olivine and plagioclase. Source: Gomes & Keil (1980).
Not reported by the Meteoritical Bulletin Database. The description and classification of the meteorite was carried out by Burragato et al. (1975). Source: Gomes & Keil (1980).
The Governador Valadares meteorite was found in 1958 by a prospector near the city that gave it its name, in the state of Minas Gerais. Unfortunately, details of the location and date of the fall are unknown and only a fragment has been found. Source: Gomes & Keil (1980).
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