Ordinary Chondrites - H Group

Synonyms: Cronstad-like chondrites; olivine-bronzite, or bronzite chondrites

General: The chondrites of the H group are named for their high content of free nickel-iron that is typical for the meteorites of this group, the "H" standing for "high iron". H chondrites contain a weight percentage of 25 to 31% total iron whereas only about 15 to 19% of the nickel-iron is found in its free, reduced form. Therefore, all H chondrites are attracted to a magnet, quite easily. Their type specimen is Cronstad, a witnessed fall from South Africa which fell in 1877.

Description: Freshly fallen H group chondrites show a dull black fusion crust, and a light colored interior with abundant sparkling metal flakes dispersed in a light grey matrix. Weathered H finds usually show dark brownish interiors, due to oxidation of the metal. The H members belong to petrological types 3 - 7, with a characteristic peak at type 5. More than 5,400 members of this group have been classified as H5, about 3,100 as H6, and just about 2,400 as H4. There are only about 600 H3s, plus several rare, and heavily brecciated H group members that contain clasts of more than one petrologic type.

Mineralogy: Besides the abundant nickel-iron metal, the primary minerals are olivine and the orthopyroxene bronzite. Therefore the chondrites of the H group have also been often called "olivine-bronzite chondrites", or "bronzite chondrites" in the past, but those names are no longer in use.

Origin & Formation: More recent comparisons of the reflectance spectra of H chondrites to the spectra of several main belt asteroids have yielded a good match – the asteroid 6 Hebe. However, Hebe might not be the direct source of the H chondrites but only some sort of ancestor. Hebe probably collided with another asteroid at one time in its history, and large parts of the S-type asteroid were dislodged into a near-Earth orbit. The resulting swarm of NEAs, the children of asteroid Hebe, are thought to be the true parent bodies from which the H chondrites are derived.

Members: This large group counts more than 12,000 members, including a lot of probable pairings from the hot deserts of Africa and Asia, as well as from the ice fields of Antarctica. Historic witnessed falls include famous meteorites such as Tabor, Barbotan, Luponnas, Pultusk, Ställdalen, or Weston. More recent, but also highly covetted witnessed falls include Juancheng, Gao, Jilin, Peekskill, Portales Valley, Thuathe, and Zag – just to name a few.