The LL chondrites are a class of stony meteorite

Meteorite

A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...

s, the least abundant group of the ordinary chondrite

Ordinary chondrite

The Ordinary chondrites are a class of stony chondritic meteorites. They are by far the most numerous group and comprise about 87% of all finds...

s, accounting for about 10–11% of observed ordinary-chondrite falls and 8–9% of all meteorite falls (see meteorite fall statistics

Meteorite fall statistics

Meteorite fall statistics are frequently used by planetary scientists to approximate the true flux of meteorites on the Earth. Meteorite falls are those meteorites that are collected after being witnessed to fall, whereas meteorite finds are discovered at a later time...

).

LL stands for Low (total) iron, Low metal. They contain 19–22% total iron and only 0.3–3% metallic iron. That means that most of the iron is present as iron oxide (FeO) in the silicates; olivine contains 26 to 32 mol% fayalite

Fayalite

Fayalite is the iron-rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system with cell parameters a 4.82 Å, b 10.48 Å and c Å 6.09.Iron rich olivine is a relatively common constituent of acidic and...

 (Fa). The most abundant minerals are hypersthene

Hypersthene

Hypersthene is a common rock-forming inosilicate mineral belonging to the group of orthorhombic pyroxenes. Many references have formally abandoned this term, preferring to categorise this mineral as enstatite or ferrosilite. It is found in igneous and some metamorphic rocks as well as in stony and...

 (a pyroxene

Pyroxene

The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...

) and olivine

Olivine

The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....

. Other minerals include Fe-Ni metal, troilite

Troilite

Troilite is a rare iron sulfide mineral with the simple formula of FeS. It is the iron rich endmember of the pyrrhotite group. Pyrrhotite has the formula FeS which is iron deficient...

 (FeS), feldspar

Feldspar

Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....

 or feldspathic glass, chromite

Chromite

Chromite is an iron chromium oxide: FeCr2O4. It is an oxide mineral belonging to the spinel group. Magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite ; substitution of aluminium occurs leading to hercynite .-Occurrence:Chromite is found in...

, and phosphates.

LL chondrites contain the largest chondrule

Chondrule

Chondrules are round grains found in chondrites. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids...

s of the ordinary chondrite groups, averaging around 1 mm diameter. The LL group includes many of the most primitive ordinary chondrites, including the well-studied Semarkona (type 3.0) chondrite. However, most LL chondrites have been thermally metamorphosed to petrologic types 5 and 6, meaning that their minerals are homogeneous in composition and chondrule borders are difficult to discern. This, together with the low content of metal, led the 19th century mineralogist Tschermak

Gustav Tschermak von Seysenegg

Gustav Tschermak von Seysenegg was an Austrian mineralogist.-Biography:He was born 19 April 1836 in Littau, Olomouc District, Moravia and studied at the University of Vienna where he obtained a teaching degree. He studied mineralogy at Heidelberg and Tübingen and obtained a PhD...

 to determine that they formed a transitional stage between chondrite

Chondrite

Chondrites are stony meteorites that have not been modified due to melting or differentiation of the parent body. They formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids...

s and achondrite

Achondrite

An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystallization on or within meteorite parent bodies...

s and to name them amphoterite

Amphoterite

Amphoterite is an obsolete term used to describe chondritic meteorites that are now classified as LL types. Most of the iron in these types of meteorites is present as ironoxide in the minerals rather than as free metal, as it is found in most other meteorites...

s. We know now that LL chondrites and achondrites are quite different, so this name is no longer in use. Many of the LL chondrites are breccias.