COOLIDGE

A very weathered mass of 4.5 kg was found by Harvey Nininger in Hamilton County, Kansas. Coolidge was originally classified as a metamorphosed member of the reduced subtype of the CV3 group due to certain similarities; 1) an abundance of FeNi-metal and troilite; 2) chondrules and refractory objects that are depleted in Na and K; and 3) a matrix composed of olivine (Noguchi, 1994). Nevertheless, significant differences exist between these chondrite types; in contrast to the reduced CV3 chondrites, Coolidge matrix is depleted in Na, chondrule compositions are different, and thermal metamorphism was greater (temperatures to ~900°C for a short duration).

Thermoluminescence (TL) sensitivity analysis was applied to Coolidge, and it was resolved as a petrologic type 4. Recent petrographic studies of Coolidge and two other meteorites, Loongana 001 and HaH 073, defined a petrologic type range of 3.8–4, implying that these meteorites are not simply metamorphosed samples of CV3 material. Recent studies of HaH 073 have found some differences in elemental abundances with Coolidge–Loongana, and they were unable to establish its classification within the Coolidge–Loongana grouplet (Huber et al., 2006). Two other recently found meteorites, NWA 779 and Sah 00177, have low-fayalite olivine compositions and refractory element abundances characteristic of this grouplet, and thus could conceivably be recognized as two additional members of the five necessary to establish a new carbonaceous chondrite group.

Only the karoondaites (CK) have petrologic type 4 members in common with the three (possibly four) Coolidge-type meteorites, but current oxidation state and bulk composition studies solidly place these meteorites in their own distinct carbonaceous chondrite grouplet. For example, the matrix of CK4 chondrites consists of both olivine and sodic plagioclase, while no plagioclase is present in Coolidge matrix. CK chondrites are not depleted in Na or K. In addition, Coolidge has a finer-grained matrix and exhibits compositional differences in spinel minerals. In contrast to Coolidge, CK chondrites are more highly oxidized as attested to by the presence of magnetite with high-Ni sulfides instead of FeNi-metal and troilite. The Coolidge grouplet is also separated by its highly fractionated moderately volatile elements, higher than all other meteorite groups. The finding of Al-rich inclusions unique from other carbonaceous chondrites also supports this classification. Coolidge has a CRE age of 37.7 m.y. The Coolidge specimen shown above is a 1.1 g cut fragment.

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