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Improving Mindat.orgRhodochrosite morphology

27th Dec 2011 16:17 UTCR. Peter Richards Expert

I happened to glance at the rhodochrosite page today, and found several inconsistencies in the descriptions of crystal morphology. Rhodochrosite, like other members of the calcite group, has a traditional morphological unit cell that is 1/4 as tall as the currently accepted unit cell based on x-ray crystallography. This latter cell is the one published on the rhodochrosite page. However, based on what I know of the common habits of rhodochrosite, all of the Miller indices listed under Morphology and Twinning appear to be appropriate only for the morphological cell. To make them consistent with the listed structural cell, the last index must be multiplied by 4 in all cases (and common multiples removed, if necessary). So, for example, {21-31} becomes {21-34}.


The same is probably true of the indices that accompany the drawings - I can't tell because the drawings don't show up on my Mac for some reason. Furthermore, the drawings use the three-index convention (omitting the third, or "i" index) whereas the Morphology section uses the full four-letter hkil notation. It would be good to be consistent here.



Similar problems probably will be found on the pages of other calcite group minerals.
 
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