The origin of faceted garnets in sandstones: dissolution or overgrowth? |
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| Authors: | AC MORTON G BORG P L HANSLEY† P D W HAUGHTON D H KRINSLEY‡ P TRUSTY‡ |
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| Institution: | Stratigraphy and Sedimentology Research Group, British Geological Survey, Keyworth, Notts NG12 5GG, UK;;Bundesanstalt fur Geowissenschaften und Rohstoffe, P.O. Box 5101 53, D-3000 Hannover 51, FRG;;Branch of Sedimentary Processes, US Geological Survey, Denver Federal Center, Denver, Colorado 80225–0046, USA;;Department of Geology, University of Glasgow, Glasgow G12 8QQ, UK;;Department of Geology, Arizona State University, Tempe, Arizona 85287–1404, USA |
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| Abstract: | Faceted garnets from a wide range of geological ages, environments and locations have been studied in polished grain mounts by a combination of backscattered electron microscopy and elemental mapping using energy-dispersive X-ray analysis. In all cases, the areas apparently showing positive relief on the faceted garnet surfaces are compositionally identical to the adjacent grain cores despite a wide variation in detrital garnet compositions. In one case, zoning within the grain core can be traced into the faceted areas on the grain surface. Thus, faceted areas must be considered to form part of the original detrital grains. Together with previously published studies on experimental garnet etching, thermodynamic conditions for garnet growth, textural relationships between faceted garnets and authigenic and detrital phases, and distribution of faceted garnets in the subsurface, this paper provides conclusive proof that faceted garnet surfaces form as a result of dissolution, not overgrowth. |
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