Ashmore meteorite, Gaines Co., Texas, USA
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|Latitude & Longitude (WGS84):||32° 53' 59'' North , 102° 16' 59'' West|
|Latitude & Longitude (decimal):||32.90000,-102.28333|
|Non-native locality type:||Meteorite|
|Meteorite Class:||H5 chondrite meteorite|
|Meteoritical Society Class:||H5|
|Metbull:||View entry in Meteoritical Bulletin Database|
|Köppen climate type:||BSk : Cold semi-arid (steppe) climate|
Ordinary chondrite (H5; S3)
Found, 1969; 55.4 kg
In February a stony meteorite was recovered from a depth of ~45 cm during deep plowing. The roughly pyramidal mass was found with an upright and well-defined conical apex. Equilibrated olivine (Fo81.2) and orthopyroxene (En 81.9) compositions and textures are characteristic of the H5 chondrite geochemical group. Primary mineral proportions are silicates (77.5 wt%), kamacite (15.3 wt%), troilite (6.3 wt%) and chromite (0.9 wt%). Plagioclase (oligoclase) composition is An12.1Ab82.3Or5.6. Minor phases include apatite, copper, graphite, ilmenite, isocubanite, and taenite (observed mostly by reflected light microscopy). Chromite occurs as subhedral grains and as scattered skeletal fragments. Plessite and sulfides are usually interstitial. Shock levels (S3) are noted, but nevertheless moderate for a meteorite. The rapid rusty alteration of freshly cut surfaces indicates that the meteorite has been severely weathered — especially in its near surface portions and along cracks. Terrestrial weatherates include both common hydrous iron oxides such as goethite and lepidocrocite as well as secondary magnetite, pentlandite, and isocubanite.
A U,Th-He age of 3.79 Ga was reported by Wasson & Wang (1991) and a relatively brief cosmic ray exposure of 2.5 Ma by Graf & Marti (1995).
Of Local Interest.
The largest mass [17.249 kg in 2000] was obtained by the Max Planck Institute (MPI) and, presumably, was transferred to the Museum für Naturkunde in Berlin when MPI disposed of their collections. However, a number of smaller specimens (100-300 g and smaller) were obtained by other institutions including the Monnig Collection (TCU) and West Texas Museum (Texas Tech.) in Texas.
12 valid minerals.
Meteorite/Rock Types Recorded
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Bryan, W. B. & Kullerud, G. (1970) Mineralogy and classification of the Ashmore chondrite: Meteoritics 5(4): p. 185. (Dec 1970).
Craig, J.R., Howie, D.A., Harris, R.L. Kullurud, G. [sic] & Bryan, W. B. (1971). The Ashmore: a new olivine-bronzite chondrite. Meteoritics 6(1): 33-37. (March 1971).
Clarke, R. S., Jr. (1972) Meteoritical Bulletin, No. 51: Meteoritics 7(2): 215-232. (June 1972).
Wasson, J. & Wang, S. (1991) The histories of ordinary chondrite parent bodies: U,Th-He age distributions. Meteoritics 26(2): 161-167. (June 1991).
Stöffler, D., Keil, K. & Scott, E.R.D. (1991). Shock metamorphism of ordinary chondrites. Geochimica et Cosmochimica Acta 55: 3845-3867. (Sept 1991).
Graf, Th. & Marti, K. (1995) Collisional history of H chondrites. J. Geophys. Res. (Planets) 100, 21247–21263.
Grady, M.M. (2000). Catalogue of Meteorites (5/e). Cambridge University Press: Cambridge; New York; Oakleigh; Madrid; Cape Town. 689 pages.