| LL chondrite | |
|---|---|
| — Group — | |
 Ragland meteorite, an LL3.4 | |
| Type | Chondrite |
| Structural classification | ? |
| Class | Ordinary chondrite |
| Subgroups |
|
| Parent body | Unknown |
| Composition | Iron 19–22% (metallic iron (Fe) 0.3–3%,iron oxide (FeO) the rest),olivine(characteristic fayalite (Fa) 26 to 32 mol%),hypersthene (apyroxene),Fe–Ni,troilite (FeS),feldspar or feldspathic glass,chromite,phosphates. |
| Petrologic type | Mostly 5 & 6 |
| Alternative names | LL chondrites, LL chondrite meteorites,Amphoterites |
TheLL chondrites are a group of stonymeteorites, the least abundant group of theordinary chondrites, accounting for about 10–11% of observed ordinary-chondrite falls and 8–9% of all meteorite falls (seemeteorite fall statistics). The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up theH chondrite,L chondrite andLL chondrite groups respectively.[1] The composition of theChelyabinsk meteorite is that of a LL chondrite meteorite. The material makeup ofItokawa, the asteroid visited by theHayabusa spacecraft which landed on it and brought particles back to Earth also proved to be type LL chondrite.
LL stands forLow (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 (Fa). The most abundant minerals arehypersthene (apyroxene) andolivine. Other minerals include Fe–Ni,troilite (FeS),feldspar or feldspathic glass,chromite, and phosphates.
LL chondrites contain the largestchondrules of the ordinary chondrite groups, averaging around 1 millimetre (0.039 in) diameter.
The LL group includes many of the most primitive ordinary chondrites, including the well-studiedSemarkona (type 3.0) chondrite. However, most LL chondrites have been thermally metamorphosed topetrologic 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 mineralogistTschermak to determine that they formed a transitional stage betweenchondrites andachondrites and to name themamphoterites.[2] We know now that LL chondrites and achondrites are quite different, so this name is no longer in use.
Many of the LL chondrites arebreccias.