Computer Science
Scientific paper
Apr 1973
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1973gecoa..37..857h&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 37, Issue 4, pp.857-858
Computer Science
3
Scientific paper
Electron microprobe analyses of the spinel mineral group, ilmenite and rutile have been carried out on part of the Luna 20 soil sample. The spinel group shows an almost continuous trend from MgAl 8 O 4 to FeCr 2 O 4 and a discontinuous trend from FeCr 2 O 4 to Fe 2 TiO 4 . Well defined non-linear relationships exist within the spinel group for Fe-Mg substitution, for divalent ( FeO / FeO + MgO ) versus trivalent ( Cr 2 O 3 / Cr 2 O 3 + A 1 2 O 3 ), and for divalent versus TiO 2 / TiO 2 + A 1 2 O 3 + Cr 2 O 3 . For Cr-Al substitution the relationship is linear and is negative for Mg-rich spinel and positive for Fe-Ti rich spinel. In general a combination of aluminous-rich chromite and ulvöspinel in the Luna 16 samples, combined with the chromian-pleonaste in Apollo 14 define comparable major compositional trends to those observed in Luna 20. Ilmenite is present in trace amounts. It is exsolved from pleonaste and pyroxene, is present in subsolidusreduced ulvöspinel and has undergone reequilibration to produce oriented intergrowths of chromite + rutile. Primary ilmenite is among the most magnesian-rieh (6 wt.% MgO) yet found in the lunar samples. The high MgO, inferred high Cr 2 O 3 concentrations and the iron content of rutile (2.5 wt.% FeO) suggest crystallization at high temperatures and pressures for some components of the Luna 20 soil.
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