Recommended classes in the Meteoritical Bulletin Database are assigned by the database editor. In most cases, this is based on the most recent classification that appears in either the Catalogue of Meteorites, MetBase, the US Antarctic Meteorite Newsletter, the Japanese Meteorite Newsletter, or the Meteoritical Bulletin. However, in a few cases it reflects differences of opinion about the proper way to classify the meteorite. The nomenclature used may also be modified by the editor to conform to an internally consistent classification scheme
The recommended classification R3.9 means:
"An R chondrite that is petrologic type 3."
The highlighted words are defined as follows:
R chondrite: The Rumuruti (R) group of chondrites does not clearly belong to any of the major classes of chondrites (ordinary, carbonaceous, enstatite); R chondrites have sub-solar Mg/Si and refractory/Si ratios, oxygen isotope compositions that plot above the terrestrial fractionation line and ordinary chondrites, and highly oxidized mineralogy.
type 3: Designates chondrites that are characterized by abundant chondrules, low degrees of aqueous alteration, and unequilibrated mineral assemblages. Many of the low-Ca pyroxene grains are monoclinic and exhibit polysynthetic twinning. The type 3 chondrites may be divided into subtypes ranging from 3.00 (least metamorphosed) to 3.9 (nearly metamorphosed to type 4 levels). If primary igneous glass occurs in the chondrules, it belongs to type 3.
Find all meteorites of type: R3.9