The crystal chemistry of armalcolites from Apollo 17
Abstract
X-ray single-crystal studies have been made of armalcolites from the 2-5-mm fraction of Apollo 17 soils 75082 and 78502. Two types of armalcolite, "ortho" and "para" have previously been distinguished on the basis of optical properties and crystal habit in the Apollo 17 samples. "Ortho"-armalcolite has the space group of pseudobrookite, Bbmm, and has cell dimensions: a = 9.743 (5); b = 10.001 (5); and c = 3.728 (2)Å. The crystal structure, refined from 582 symmetry-independent intensities, is ordered with Ti in the site with m symmetry and Mg and Fe in the site with mm symmetry. "Para"-armalcolite has space group Bbmm, cell dimensions: a = 9.712 (20), b = 9.997 (20), and c 3.735 (8)Å; and is structurally identical with "ortho"-armalcolite. The two crystals studied are similar but not identical in composition, but the slight compositional differences and identical structures do not warrant the use of separate mineral names.
- Publication:
-
Earth and Planetary Science Letters
- Pub Date:
- December 1974
- DOI:
- 10.1016/0012-821X(74)90104-6
- Bibcode:
- 1974E&PSL..24..262S
- Keywords:
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- Apollo 17 Flight;
- Crystal Structure;
- Lunar Composition;
- Lunar Soil;
- Chromium Oxides;
- Magnesium Oxides;
- Optical Properties;
- Single Crystals;
- X Ray Analysis