L chondrites
Low-iron ordinary chondrites: the single most common group of meteorites.
- Classification
- Stony meteorites › Chondrites › Ordinary chondrites › L chondrites
- Share of witnessed falls
- about 37%
- In our catalogue
- 16,101 meteorites, 394 seen to fall
- Heaviest
- Northwest Africa 869, 2 t
- Earliest recorded fall
- Nogata, 860
- Most recent fall
- Battle Mountain, 2012
L chondrites have less metal than H chondrites, typically 4% to 10%, and more iron in their olivine (about 23–26 mol% fayalite). They are the most common group of all, around 37% of falls.
Many L chondrites are heavily shocked and show gas-loss ages of about 470 million years. They record the break-up of their parent asteroid in a huge collision in the Ordovician period. Fossil L chondrites found in Swedish limestone of that age show that Earth was showered with this debris for millions of years afterwards.
Mineralogy and chemistry
The same minerals as H chondrites appear in different proportions: more olivine, less metal and more iron in the silicates. Total iron is about 22% by weight, and olivine contains about 22–26 mol% fayalite, with pyroxene at about 19–22 mol% ferrosilite. Chondrules average around 0.7 mm. Type 6 is the most common, and many L chondrites are shocked to stage S4 or higher, with dark melt veins and black, shock-darkened silicates.
Their oxygen isotopes sit just above the terrestrial line, with a Δ17O of about +1.1 per mil, between H and LL. A small number of stones fall between groups and are labelled H/L or L/LL.
Parent body and a giant collision
About 466 million years ago, in the Ordovician period, the L chondrite parent asteroid was shattered in one of the largest collisions in the asteroid belt in the last few billion years. Argon in many L chondrites was driven out by the heat of that event, resetting their ages. Debris flooded the inner Solar System: limestone quarries at Kinnekulle in southern Sweden contain more than a hundred fossil meteorites, all L chondrites, and layers of the same age around the world are rich in chromite grains from them. Some researchers link the dust from this break-up to a cooling of Earth's climate at the time.
Studies of asteroid families point to the Massalia family in the inner main belt as the likely source of the L chondrites reaching Earth today.
Abundance and famous examples
L chondrites are the most common group of meteorites, about 37% of witnessed falls. There is no type specimen, as the group is defined by its chemistry. L'Aigle (L6) fell as about 3,000 stones in Normandy on 26 April 1803, and Jean-Baptiste Biot's report on it settled that meteorites come from the sky. Barwell (L5) fell on a Leicestershire village on Christmas Eve 1965. Mocs, Romania, 1882, and Kunashak, Russia, 1949, were big showers; Bruderheim (L6), Canada, 1960, and Park Forest (L5), a Chicago suburb, 2003, were well-recorded falls. Valera (L5), Venezuela, 1972, is reported to have killed a cow.
How to recognise one
L chondrites look much like H chondrites but have fewer and smaller metal flecks on a cut face, and they pull less strongly on a magnet. Heavily shocked examples are often veined with thin black lines of melt or are dark grey throughout. Group assignment needs a measurement of the olivine.
Famous examples
- L'Aigle L6, France, 1803 · 37 kg
- Barwell L5, United Kingdom, 1965 · 44 kg
- Valera L5, Venezuela, 1972 · 50 kg
- Claxton L6, United States, 1984 · 1.46 kg
- Mbale L5/6, Uganda, 1992 · 150 kg
Related groups
- H chondrites High-iron ordinary chondrites: about a third of all meteorites seen to fall.
- LL chondrites Low iron, low metal: the ordinary chondrites matched to asteroid Itokawa.
- 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).