Summary: Seven manganese minerals have been observed in geodes from Chihuahua, Mexico. Ramsdellite occurs in a number of different habits, but the morphology and precession X-ray patterns suggest that it is pseudomorphous after groutite. Pyrolusite is found only in association with rams-dellite and is believed to be an alteration product of that mineral. Todorokite generally occurs as a late-stage fibrous overgrowth in many of the geodes. Ranciéite, birnessite, hollandite, and cryptomelane are present in trace amounts. This assemblage of manganese minerals is typical of supergene mineralization.
Mineralogical Magazine; March 1974 v. 39; no. 305; p. 549-558; DOI: 10.1180/minmag.1974.039.305.07
© 1974, The Mineralogical Society
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