Pinnaroo meteorite, Pinnaroo, Murray Mallee, Murray Basin, South Australia, Australiai

Regional Level Types
Pinnaroo meteorite	Meteorite Fall Location
Pinnaroo	- not defined -
Murray Mallee	- not defined -
Murray Basin	Basin
South Australia	State
Australia	Country

Stony-iron, Mesosiderite-A4
Find, 1927; 39.4 kg, a single mass

An unusual, rather large and roughly ellipsoidal mass (~37x29x17 cm) was plowed up 15 km from Pinnaroo. It was brought to the University of Adelaide for identification where it was sectioned into 3 pieces. The initial assay — silicates (51 vol%), metal (44 vol%), and troilite (4.5 vol%) — revealed a severely weathered stony-iron meteorite with some unusual features. Both the metal and silicates are found in the usually fine-grained matrix and as larger irregular grains and crystals. Masswise, of course, the Fe-Ni metal (Ni 7%) constitutes most of the meteorites mass (~60 wt%). The metal, mostly Kamacite, display a Widmanstätten pattern with prominent kamacite bands accompanied by narrow taenite ribbons in larger metallic nodules and is also present as very fine kamacite-taenite intergrowths within the matrix. The silicates are predominantly orthopyroxene (50%) and anorthitic plagioclase (~40%), but some of the larger olivine crystals draw immediate attention. Troilite (~10 wt%) is also prominent. All major components — Fe-Ni metal, silicates, and troilite — occur as clasts as well as matrix. Minor and trace constituents include additional silicates (augite, pigeonite, tridymite), phosphates, and several opaques. The troilite, often simultaneously contingent to both silicates and metal, is one of numerous signs that the Pinnaroo mass has been shock-melted. All mesosiderites are breccias of one sort or another, but of the ~40 fully classified mesosiderites only 7 have been characterized as petrologic type 4 (shock-melted).

Some caution is required in interpreting modal and volume analyses. Lawrencite and pentlandite in iron-rich meteorites are common products of terrestrial weathering and Pinnaroo is severely weathered on both the outside and in some interior regions. In this context, the observations of fragile oldhamite and daubréelite are mildly surprising, but not totally unexpected as weathering may be unusually irregular in brecciated meteorites.

Pinnaroo is classified as an Mesosiderites-A4 (high in plagioclase). Among the ~ 40 fully classified mesosiderites, Pinnaroo is the most massive of the 4 meteorites classified as mesosiderite-A4. Most of the mass (~25 kg) is with the University of Adelaide with less than 2 kg distributed among other scientific parties as of 2000.

Other Regions, Features and Areas containing this locality

References