Angra dos Reis meteorite, Ilha Grande, Angra dos Reis, Rio de Janeiro, Brazili

Regional Level Types
Angra dos Reis meteorite	Meteorite Fall Location
Ilha Grande	- not defined -
Angra dos Reis	Municipality
Rio de Janeiro	State
Brazil	Country

Angrite, S1; W0 (differentiated achondrite)
Fall, 30 January 1869; 1500 g
Angrite prototype: Only angrite Fall, 4th most massive angrite


The Angra dos Reis (stone) fell into a bay and was recovered from a depth of 2 m the following day. In good time it was recognized as a unique meteorite. Fassaite, a Ti-rich variety of augite, is its dominant constituent (93 vol%) — mostly as a dense mass of grains meeting at triple junctions. Angra dos Reis is not quite, however, a monominerallic rock. It contains a number of minor accessory minerals — including olivine, kirschteinite, Ti-rich magnetite, and plagioclase plus small amounts of troilite and Fe-Ni metal. Several of the mineral phases are unusually rich in both aluminium and calcium. Prinz et al. (1977) provided a comprehensive survey of the unique Angra dos Reis mineralogical assemblage.

After the recovery of the large 16 kilogram D'Orbigny meteorite in 1979 and several smaller Antarctic finds, the Angra dos Reis (stone) meteorite was designated as the prototype for the Angrite class of achondritic meteorites. Angrites are characterized by their low alkali contents, high Ca/Al ratios, and a somewhat variable but still distinctive mineral assemblage (e.g., various Ca, Al, &/or Ti-rich phases). As of mid 2015 Angra dos Reis still remains the only witnessed angrite fall.

Angra dos Reis and the other angrites are also very ancient. The age of formation for its mineralogical assemblage was ~4.558 billion years ago; several other angrites are ~5 million years older than that. Putatively the Angra dos Reis parent body was metamorphically active for five or so million years before the remnant radioactivities of planetismal formation died out.

Technical Note #1. In meteoritic literature the terms ‘whitlockite’ and ‘merrillite’ often refer to the same mineral — anhydrous Ca-Phosphate — as phosphate mineral definitions have been redefined more than once. Formally, ‘Merrillite’ is defined as extraterrestrial Whitlockite. However, the reader should be warned. Most ‘anhydrous’ terrestrial phosphates are not quite so free of water as some varieties of meteoritic ‘merrillite’. The phosphates of angrites are critical components in current refinements of Angrite chronology.

Technical Note #2. The proper name for the meteorite is ‘Angra dos Reis (stone)’ which is to be distinguished from ‘Angra dos Reis (iron).’ ‘Angra dos Reis (iron)’ is a synonym for an apparently mislabled piece of the Pirapora iron meteorite.

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