LL chondrites
Low iron, low metal: the ordinary chondrites matched to asteroid Itokawa.
- Classification
- Stony meteorites › Chondrites › Ordinary chondrites › LL chondrites
- Share of witnessed falls
- about 8.2%
- In our catalogue
- 5,896 meteorites, 85 seen to fall
- Heaviest
- Paragould, 408 kg
- Earliest recorded fall
- Ensisheim, 1491
- Most recent fall
- Chelyabinsk, 2013
LL chondrites have the least metal of the ordinary chondrites, only about 1% to 3%, and the most iron in their olivine (about 27–32 mol% fayalite). They make up about 8% of falls. Their chondrules are on average the largest of the ordinary chondrites.
In 2010 the Hayabusa spacecraft returned dust from asteroid 25143 Itokawa, and it proved to be LL chondrite material. The 2013 Chelyabinsk fireball, which injured around 1,500 people in Russia mostly with broken glass, was an LL chondrite.
Mineralogy and chemistry
LL chondrites have the least metal of the ordinary chondrites and the most iron-rich silicates. Total iron is about 19–20% by weight, and much of it sits in olivine (about 26–32 mol% fayalite) rather than in metal. What metal there is tends to be richer in nickel and cobalt. Chondrules are the largest of the ordinary chondrites, averaging close to 0.9 mm, and the rock is rich in olivine.
Oxygen isotopes are the highest of the three ordinary groups, with a Δ17O of about +1.3 per mil. Some of the least altered chondrites of all belong here: Semarkona, which fell in India in 1940, is classified LL3.00 and preserves chondrules and matrix almost untouched by heat, which makes it a standard for studying the early Solar System.
Parent body: asteroid Itokawa
The Japanese Hayabusa spacecraft collected about 1,500 tiny grains from the surface of the near-Earth asteroid 25143 Itokawa in 2005 and brought them back in 2010. Their mineral compositions and oxygen isotopes matched LL chondrites, mostly the strongly heated types 5 and 6. Itokawa is a small rubble pile about 535 m long, made of fragments of a once larger body. This was the first time a meteorite group was tied to a particular asteroid by direct sampling. The Flora family in the inner main belt has been suggested as a major source of LL material.
Abundance and famous examples
About 8% of witnessed falls are LL chondrites. There is no type specimen. Ensisheim (LL6), which fell in Alsace on 7 November 1491, is the oldest witnessed fall with material still preserved; a large piece is kept in the town. Saint-Séverin (LL6), France, 1966, yielded about 271 kg. The Chelyabinsk fireball of 15 February 2013 came from an LL5 asteroid about 19 m across, the largest known object to hit Earth's atmosphere since Tunguska in 1908. Bjurböle, Finland, 1899, and Holbrook, Arizona, 1912, are classed between L and LL.
Related groups
LL chondrites sit at the oxidised end of the ordinary chondrite sequence, closest in composition to the R chondrites, which carry still more iron in their olivine and almost no metal. Stones that fall between L and LL, such as Bjurböle and Holbrook, are thought to be either members of a continuous range or samples of yet another parent body. Like the H and L groups, LL chondrites show the full range of petrologic types from 3 to 6, and their unequilibrated type 3 members are the most studied ordinary chondrites for clues to how chondrules formed.
How to recognise one
Expect large, easily seen chondrules, few metal grains and only a modest pull on a magnet. LL chondrites are often breccias with light and dark fragments. Fresh falls have a black crust; weathered finds can be pale, because there is little metal to rust.
Famous examples
- Chelyabinsk LL5, Russia, 2013 · 100 kg
- Ensisheim LL6, France, 1491 · 127 kg
- Semarkona LL3.00, India, 1940 · 691 g
- Saint-Séverin LL6, France, 1966 · 271 kg
- Kilabo LL6, Nigeria, 2002 · 19 kg
Related groups
- L chondrites Low-iron ordinary chondrites: the single most common group of meteorites.
- H chondrites High-iron ordinary chondrites: about a third of all meteorites seen to fall.
- Ordinary chondrites The everyday meteorite: four in every five falls. Three groups, H, L and LL, from at least three asteroids.
Photos shared under Creative Commons licences (Wikimedia Commons).