MS-I7-P248 micrometeorite, Schirmacher Oasis, Northern Gruber Mountains, Queen Maud Land, East Antarctica, Antarcticai

Regional Level Types
MS-I7-P248 micrometeorite	Meteorite Fall Location
Schirmacher Oasis	Glacier
Northern Gruber Mountains	Mountain Range
Queen Maud Land	Region
East Antarctica	Region
Antarctica	Continent

The particle MS-I7-P248 is a silicate-type (S-type) spherule ∼80 µm in diameter surrounded by a magnetite rim (Fig. 1). It has a porphyritic texture and has significant coarse magnetite crystallites. There are only a few vesicles present, which are small and irregularly shaped. The spherule has a mottled texture, and mineralogy is comprised mainly of Ca-pyroxene, which is chemically homogeneous. Magnetite grains are interstitial and identified as unusual skeletal growth morphologies such as skeletal cubic, cruciform type but also occur in larger cubic crystals, unlike those symplectic, cellular, long spreading dendritic, small euhedral cubic crystal morphologies commonly observed in S-type porphyritic and barred olivine cosmic spherules. Magnetite is also observed filling as a thin line along microfractures in this spherule. The Ca-pyroxene in MS-I7-P248 with a composition of Wo37-41En25-27Fs34-36 represents a ferroaugite.
articles surrounded by a magnetite rim suggest extraterrestrial origin, formed during heating in the atmospheric entry. This entry heating is similar to any of the cosmic spherules. However, the texture and mineralogy of MS-I7-P248 differ from the most common chondritic cosmic spherules. The texture of MS-I7-P248 is similar to S-type porphyritic spherules but is not comparable to glass textures previously reported in achondrite spherules. MS-I7-P248 is uniquely dominated by Ca-rich pyroxene, mainly as a ferroaugite. In addition, the spherule also contains accessary magnetite crystallites with unusual morphologies, such as skeletal cubic, which were not observed before in cosmic spherules. Augite in MS-I7-P248 exhibits molar Fe/Mn vs. Fe/Mg values associated with the lunar source.

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References