H chondrite
H chondrites are ordinary chondrites with the highest content of iron and metal.
The H chondrites are one of the three groups of ordinary chondrites, and the "H" stands for high total iron. They contain the most iron-nickel metal of the three groups, often around a sixth to a fifth of the rock by weight, and their olivine contains relatively little iron. Geologists express this as the fayalite content (Fa): about Fa16 to Fa20 in H chondrites, compared with higher values in L and LL chondrites.
H chondrites are among the most common meteorites. Their cosmic-ray exposure ages, which measure how long they travelled in space as small bodies, cluster strongly near 7 to 8 million years, suggesting that one major collision sent many of them on their way to Earth. Peekskill, the H6 chondrite that hit a parked car in New York State in 1992, and Sylacauga, the H4 stone that struck a woman in Alabama in 1954, are both H chondrites.
In hand specimen, H chondrites are typically heavy for a stone and strongly magnetic. A cut face shows abundant small grains of bright metal scattered through grey matrix. Chemical analysis of olivine or of the oxygen isotopes confirms the group.
Related terms
Level: Enthusiast Teens and adults