Types of Meteorites

Chondrites are the most common type of meteorite, with over 70,000 chondrites classified and recorded in the global meteorite collection. These are stony meteorites made of spherical blobs (chondrules) of the minerals olivine and pyroxene with varying amounts of iron-nickel metals, as well as smaller amounts of other minerals and sulfides. 

The majority of chondrites are what we call "ordinary chondrites" because they are by far the most abundant type of chondrite and meteorite, but there is also a smaller group called "enstatite chondrites". Enstatite chondrites don't contain any olivine and instead are made mostly from a magnesium-rich pyroxene (enstatite), and can also include some uncommon types of sulfide and even presolar minerals!

Carbonaceous chondrites come from the outer solar system and contain chondrules as well as hydrated minerals and calcium-aluminium-rich inclusions (CAIs). These CAIs are the oldest solids in the solar system having been dated to 4568 million years ago.

These meteorites are particularly fascinating because they contain water, organic molecules, and amino acids - the building blocks for life! That doesn't mean that we've found aliens in meteorites yet, but studying these meteorites might help us understand how life may have gotten started on Earth.

Achondrites are formed through the melting and recrystallization of chondrites, recording important igneous and metamorphic processes during the evolution of planetary bodies and  often look very similar to basalts that we find on Earth. We further can sub-divide achondrites into "primitive achondrites" and "evolved achondrites". Primitive achondrites represent the start of melting and have the same mineral compositions as chondrites, but evolved achondrites record long-lasting igneous activity.

An interesting part about studying achondrites is that we know where most of them are from! We have achondrite meteorites from the Moon, from Mars, and from the large asteroid Vesta. Sample return missions to the Moon and Mars help scientists understand these meteorites in context of their home and can provide key insights into the history of our nearest planetary neighbors. 

Although we have lots of different categories and classifications for meteorites, not all meteorites fit nicely into them! Meteorites that have unusual compositions, appearances, or isotope signatures get called "anomalous" or "ungrouped". These meteorites are less common, but can often give us clues about the evolution of the solar system that we wouldn't otherwise find!