angrites

Angrites are a small and scientifically important group of achondritic meteorites with basaltic compositions that originated on a differentiated asteroid or planetary body early in the solar system’s history. They are among the oldest known igneous rocks, with crystallization ages around 4.56 billion years ago, and they provide key constraints on early planetary differentiation and crust formation.

The name Angrite derives from the first specimen described, the Angra dos Reis meteorite, which fell in Brazil in 1869. Other well-known angrites include samples such as D’Orbigny and Sahara 99555, which have been studied to illuminate the thermal and magmatic evolution of their parent body. Angrites are typically preserved as basaltic to andesitic rocks, with mineral assemblages dominated by calcium-rich pyroxene (augite), plagioclase (often Ca-rich), and olivine, along with various oxides and accessory minerals. Textures span well-preserved cumulate grains to rapidly quenched, glassy forms, reflecting a range of cooling histories on or near the parent body’s surface.

Petrogenetically, angrites record rapid early magmatic differentiation in a small body, rather than on a Moon- or Earth-sized planet. Their isotopic systems, especially aluminum-magnesium and lead-lead chronometers, have been used to place tight ages on early solar system processes and to compare the timing of differentiation among early planetary bodies.

Angrites are studied to understand the earliest crust formation, the timing of core formation on small bodies, and the thermal evolution of planetesimals. They remain among the most debated and informative samples of the solar system’s first few tens of millions of years.