Saturday, December 20, 2008

Mineralogy of Sunset Crater fumarole deposits

The summit of Sunset Crater has been closed to hikers since 1973, and getting access to the fumarole deposits requires special permission. Sarah Hanson, a professor at Adrian College, has worked for the Park Service for the past 5 summers at the Monument and is lead author on a new report describing the mineralogy of the fumarole deposits. Sarah sent us a copy of Rocks & Minerals magazine, Nov-Dec issue with an 11-page article filled with SEM photos of the minerals.

The six fumarole deposits are narrow, elongate and parallel to the crater rim. Sarah and co-authors conclude the fumarole vents were active in the waning stages of volcanic activity (which began during the period of 1073-1090 A.D.) with cooling vapors and increasing oxygen fugacity, resulting in a zoning of minerals from gypsum-hematite-magnetite to gypsum-earthy hematite to gypsum-sulfur.

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