Stony meteorites consist predominately of silicon-based minerals that form rock. They are the most abundant type of meteorite with about 95% of meteorite falls belonging to this group. They are divided into two subgroups: chondrites and achondrites. Here we talk about achondrites – there is a different post for chondrites here.
1. Achondrite
Achondrites are stony meteorites that do not contain chondrules. Their material has been differentiated due to melting and recrystallization in large parent bodies. They account for about 6.5% of stony and 6% of all meteorites. It is a complex group that contains meteorites from diverse locations throughout our Solar System. There are divided in lunar, martian, asteroidal and primitive.
1.1. Lunar
Lunar meteorites result from another meteorite hitting the Moon, causing it to release its rocks at escape velocity into space. They go into orbit for probably millions of years until their trajectory led them to land on Earth. These meteorites are known to be from the Moon because lunar rocks were collected and brought to Earth by the Apollo missions. Their composition was tested, and it was scientifically proven that they cannot have originated in any part of the Solar System other than our Moon. Although the Moon is our nearest celestial body, lunar meteorites are extremely rare due to the chain of events necessary for them to find their way to Earth. Only 0.6% of all known meteorites are lunar and there has never been an observed fall of a lunar meteorite. Now, however, you can have a piece of the Moon in your hands.
1.2. Martian
Martian meteorites result from another meteorite hitting Mars, causing it to release its rocks at escape velocity into space. They go into orbit for probably millions of years until their trajectory led them to land on Earth. These meteorites are known to be from Mars because they have tiny bubbles of air that are unequivocally similar to the Martian atmosphere as studied in-situ by Viking landers. There are 3 main types of Martian meteorites: Shergottites, Nakhlites and Chassignites that form the SNC group. There are others types that are much rarer with only 1 meteorite. Although Mars is our third nearest celestial body, Martian meteorites are extremely rare due to the chain of events necessary for them to find their way to Earth. Only 0.4% of all known meteorites are Martian.
1.3. Asteroidal
This group comprises achondrites that come from large differentiated parent bodies where their mineralogical and chemical composition were changed by melting and crystallization processes. There are 3 groups: the HED clan, angrites and aubrites.
1.3.1. HED
This group of meteorites come from Asteroid Vesta, a huge asteroid in the asteoroid belt, between Mars and Jupiter. A great impact occurred in the South hemisphere of Vesta less than 1 billion years ago, ejecting rocks from the asteroid into space. Eventually, some of these rocks fell on Earth. HED is an acronym for the meteorites that comprise this clan: Howardites, Eucrites, and Diogenites. The HED clan accounts for only 3% of all known meteorites.
1.3.1.1. Eucrite
Eucrites are the most common type of achondrite and account for roughly 50% of the HED clan. They may be distinguished from other stony meteorites by their shiny dark brown to black fusion crust which gives them a glassy luster. Eucrites come from the outermost crust of asteroid Vesta.
1.3.1.2. Diogenite
Diogenites are named for the fifth century B.C. Greek philosopher, Diogenes of Apollonia, considered to be the first person to suggest that meteorites actually come from beyond Earth. Their origin appears to be plutonic, from deep below the eucrite crust of the asteroid Vesta.
1.3.1.3 Howardite
Howardites are essentially a mixture of the other two types, where more than 10% of the least abundant type is present.
1.3.2. Angrite
They are basaltic rocks composed mostly of the mineral augite. They can be porous, which is a rare feature among meteorites. Angrites are named after the Angra dos Reis meteorite, which fell in Brazil in 1869.
1.3.3. Aubrite
Aubrites are sometimes referred to as enstatite achondrites due to their almost monomineralic enstatite pyroxenite content. They have an igneous origin, and this means they originated in an asteroid. Aubrites are named after the Aubres meteorite, which fell in France in 1836.
1.4. Primitive
This group comprises achondrites whose chemical composition is primitive in the sense that it is similar to the composition of chondrites, but their texture is igneous, indicative of melting processes. There are 4 groups: brachinites, the acapulcoite-lodranite family, ureilites and winonaites.
1.4.1. Brachinite
Brachinites are a group of meteorites that are classified either as primitive achondrites or as asteroidal achondrites. Like all primitive achondrites, they have similarities and differences with both chondrites and achondrites. Brachinites contain between 74% and 98% olivine by volume. Brachinites are named after the Brachina meteorite, which was found in Australia in 1974.
1.4.2. Acapulcoite-Lodranite family
These are closely related to each other and equigranular meteorites. Acapulcoites have a finer grain than lodranites. Acapulcoites are named after the meteorite that fell in Acapulco, Mexico in 1913. Lodranites are named after the meteorite that fell in Lodran, Pakistan in 1868.
1.4.3. Ureilite
Ureilites are composed mostly from olivine and pyroxene. However, they are especially noteworthy due to their composition of around 3% carbon, in the form of graphite and nanodiamonds. They are named after the Novo-Urei meteorite that fell in Russia in 1886. The Novo-Urei meteorite was broken apart and partly eaten by witnesses of the fall.
1.4.4. Winonaite
Winonaites are fine to medium grained, mostly equigranular, and contain ferric sulfide. They are closely related to the silicate inclusions found in IAB and IIICD irons. Winonaites are named after the meteorite that was found in Winona, USA in 1928. This meteorite was located in a native American stone burial cist, so it was likely highly revered. It probably fell between 1070 and 1275.
Additional resources
Click on the link to learn about impactites: Information About Impactites.
For a detailed guide on identifying meteorites visit: How to Identify a Meteorite.
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