Ordinary Chondrites - L Group

Synonyms: Baroti-like chondrites; olivine-hypersthene, or hypersthene chondrites

General: The L group chondrites are named for their relatively low content of nickel-iron in its free form – the "L" standing for "low iron". They contain a weight percentage of 20 to 25% total iron, but only 4 to 10% of the nickel-iron is found as free metal. Therefore, the L chondrites are also attracted to a magnet, but less than their cousins of the H group. Their type specimen is Baroti, a witnessed Indian chondrite fall from 1910.

Description: Fresh L members resemble H chondrites, with dull black fusion crusts, and light grey interiors, but their matrix contains considerably less metal flakes. The L chondrites belong to petrologic types 3 – 7, with a characteristic peak at type 6. More than 5,600 have been classified as L6, about 2,800 as L5, just about 850 as L4, and only about 600 as L3. Brecciated L members that show clasts of several petrologic types, and other unusual members make up for the rest.

Mineralogy: Besides magnetite and nickel-iron, the L members are primarily composed of olivine, and the orthopyroxene hypersthene. Consequently, they have been called "olivine-hypersthene", or "hypersthene chondrites" in older literature. However, these terms are no longer in use.

Origin & Formation: It has been suspected that the L chondrites might be derived from near-Earth asteroid 433 Eros which has been intensely studied by space probe NEAR-Shoemaker, more recently. The reflectance spectra of Eros and L chondrites seem to match closely – however, most L group members show signs of severe shock metamorphism, suggesting a violent history for their parent body. Maybe the real parent body of the L chondrites was some kind of relative, or even a former part of Eros that has been completely disrupted when it collided with another asteroid.

Members: With about 10,500 members, including many probable pairings from the hot and cold deserts, the chondrites of the L group represent the second largest group of ordinary chondrites. Historic witnessed falls include famous meteorites such as Mezö-Madaras, Wold Cottage, Alfianello, and L'Aigle. More recent, but also highly covetted witnessed falls include Barwell, Claxton, La Criolla, Mbale, Monze, or Park Forest – just to name a few. Desert finds are abundant, such as SaU 001, a very nice L find from Oman, or NWA 869, a rather fresh brecciated L4-6 chondrite from Northwest Africa.