Angra dos Reis meteorite

Angra dos Reis
Type	Achondrite
Group	Angrite
Composition	Fassaite (93%)
Country	Brazil
Region	Angra dos Reis
Coordinates	22°58′S 44°19′W
Observed fall	Yes
Fall date	20 January 1869
TKW	1.5 kilograms (3.3 lb)

The Angra dos Reis meteorite is the type specimen of the angrite group. It was observed when it fell to earth in 1869.

Discovery and naming

The meteorite is named after Angra dos Reis, a municipality of Rio de Janeiro, Brazil. It fell on 20 January 1869 into the bay where the water was about 2 m deep. Two fragments were found by a diver the next day.

Mineralogy

Although it is the type specimen of the angrites, Angra dos Reis is actually very different to most angrites. It is almost completely made from a rare form of pyroxene called fassaite. This makes the it more like a pyroxenite, than the typical angrite which is similar to a basalt. The only other meteorite samples that contain fassaite are the Calcium-aluminium-rich inclusions found in the Allende meteorite. The reason for this exotic composition is thought to be partial melting of a chondritic precursor under redox conditions in which meteoric iron is unstable.