F Group (Forsterite Chondrites)
Synonyms: forsterite chondrites
General: This strange grouplet is known solely from certain lithologies, i.e., from certain xenolithic inclusions that have been found in two achondrites, both members of the aubrite group: Allan Hills 78113 from Antarctica, and Cumberland Falls, a meteorite that fell in Kentucky, USA, in 1919.
Description: Both are polymict breccias that contain dark clasts of chondritic material that does not fit into any established chondrite group or clan. Those clasts have been provisionally named for the fact that the olivine found in these lithologies consists of the pure magnesium-rich end-member of olivine called forsterite. Hence, the grouplet was named forsterite group or F chondrites.
Mineralogy: All F lithologies are highly unequilibrated and can be assigned to petrologic type 3. Their mineralogy and oxidation state places the F chondrites between the H group of the ordinary chondrites and the E chondrites.
Formation history & Origin: When it comes to their origin, it is believed that they are derived from a small and primitive asteroid of F chondritic composition that collided with the aubrite parent body short after their formation in the early solar system.
Members: Xenolithic (F chondritic) inclusions in Allan Hills 78113, and Cumberland Falls.