The Angra dos Reis meteorite is the type specimen of the

angrite Angrites are a rare group of achondrites consisting mostly of Al-Ti bearing diopside, hedenbergite, olivine, anorthite and troilite with minor traces of phosphate and metals. The group is named for the Angra dos Reis meteorite. They are the olde ...

group. It was observed when it fell to earth in 1869.

Discovery and naming

The meteorite is named after

Angra dos Reis Angra dos Reis (; Portuguese for ''cove'' or ''bay of the Kings'') is a Brazilian municipality located in the southern part of the state of Rio de Janeiro. The city is located by the sea and includes in its territory many offshore islands, the l ...

, a municipality of

Rio de Janeiro Rio de Janeiro ( , , ; literally 'River of January'), or simply Rio, is the capital of the state of the same name, Brazil's third-most populous state, and the second-most populous city in Brazil, after São Paulo. Listed by the GaWC as a b ...

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

. It fell on 20 January 1869 into the bay where the water was about 2 meters deep. Two fragments were found by a diver the next day.

Museum

The

National Museum of Brazil The National Museum of Brazil ( pt, Museu Nacional) is the oldest scientific institution of Brazil. It is located in the city of Rio de Janeiro, where it is installed in the Paço de São Cristóvão (Saint Christopher's Palace), which is in ...

holds the meteorite as part of its meteorite collection. After the museum's 2018

fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. At a certain point in the combustion reaction, called the ignition ...

, there were concerns that it was lost in the rubble of the museum. Some meteorites were found on October 19, 2018, including the ''Angra dos Reis''.

Mineralogy

Although it is the type specimen of the

s, Angra dos Reis is actually very different from most other angrites. It consists almost entirely of a rare form of

pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...

called

fassaite Fassaite is a variety of augite with a very low iron content, . It is named after the Fassa Valley, Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in ...

. This makes it more like a

pyroxenite Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite, diopside, hypersthene, bronzite or enstatite. Pyroxenites are classified into clinopyroxenites, orthopyroxenites, and the websteri ...

than the typical

, which is similar to a

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

. The only other meteorite samples that contain

are the calcium-aluminium-rich inclusions found in the

Allende meteorite The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 01:05 on February 8, 1969, falling over the Mexican state of Chihuahua. After it broke up in the atmosphere, an extensive search for ...

. The reason for this exotic composition is thought to be partial melting of a chondritic precursor under reduction-oxidation (

redox Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate (chemistry), substrate change. Oxidation is the loss of Electron, electrons or an increase in the oxidation state, while reduction ...

) conditions in which

meteoric iron Meteoric iron, sometimes meteoritic iron, is a native metal and early-universe protoplanetary-disk remnant found in meteorites and made from the elements iron and nickel, mainly in the form of the mineral phases kamacite and taenite. Meteoric iro ...

is unstable.

References

{{Meteorites by name 1869 in Brazil Meteorites found in Brazil National Museum of Brazil