Angrite

Angrites are a rare type of achondrite meteorite. They are basaltic in composition and represent some of the oldest and most magnesian igneous rocks known. Angrites are important for understanding the early differentiation and magmatic processes of planetesimals in the early solar system.

Origin and Characteristics:

The origin of angrites is still debated, but they are believed to have originated from a differentiated asteroid, sometimes referred to as the "Angrite Parent Body" (APB). This asteroid likely underwent partial or complete melting early in its history, leading to the formation of a basaltic crust or near-surface layer from which angrites were derived.

Angrites are characterized by their coarse-grained texture, dominated by the minerals olivine, pyroxene (specifically, fassaite), and plagioclase (specifically, anorthite). They also contain minor amounts of other minerals, such as ulvöspinel, troilite, and phosphates. Their high abundance of calcium and aluminum, along with their low abundance of volatile elements, distinguishes them from other types of basaltic meteorites, such as eucrites.

Age and Significance:

Angrites are among the oldest solar system materials known, with radiometric dating indicating formation ages of approximately 4.55 billion years. This makes them valuable for studying the earliest stages of planetary formation and differentiation. Their age also provides constraints on the timing of accretion and melting processes in the early solar system.

Types of Angrites:

Angrites are typically divided into two main groups based on their textures and mineral compositions:

• Plutonic Angrites: These have a coarse-grained texture and represent slowly cooled magmas. They are thought to have formed deeper within the Angrite Parent Body.

• Volcanic Angrites: These have a finer-grained texture and may contain vesicles (small gas bubbles), indicating they formed from rapidly cooled lavas on the surface of the Angrite Parent Body.

Examples of Angrites:

Notable examples of angrites include Angra dos Reis (the first angrite discovered), D'Orbigny, Sahara 99555, and NWA 4590. These meteorites have been extensively studied to understand their petrology, geochemistry, and geochronology.