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Summary
| Description |
Merumite (largest specimen's long axis is 8.5 mm across) from Director Creek in northwestern Guyana (British Guiana), northern South America. Merumite is the "rarest rock on Earth". It only occurs as small, loose alluvial grains in the upper branches of Director Creek in northwestern Guyana (= northern South America). Merumite rocks are finely crystalline mixes of chromium minerals of inferred hydrothermal origin. The principal minerals in merumite are eskolaite (Cr2O3), guyanaite (CrO·OH), bracewellite (CrO·OH), grimaldiite (CrO·OH), mcconellite (CuCrO2), chromian pyrophyllite, and quartz. Trace minerals include chromium gahnite (Zn(Al0.7Cr0.3)2O4) and native gold (Au). The geologic provenance of merumite rocks is uncertain, but they are possibly derived from the Roraima Formation, a Paleozoic? succession of coarse-grained siliciclastic sedimentary rocks and volcanic ash beds. The Roraima Formation is now eroded away in the Director Creek area. Locality: loose alluvial grains in the upper branches of Director Creek (a small tributary of the Merume River) (possibly from a 3 to 4.5 meter wide & 3 kilometer long stretch of Director Creek along the eastern base of Robello Ridge), north of the Pakaraima Plateau/Karanang Mountains, ~16 km southwest of Kamakusa, northwestern Guyana (British Guiana), northern South America. Info. synthesized from: Milton et al. (1976) - Merumite - a complex assemblage of chromium minerals from Guyana. United States Geological Survey Professional Paper 887. 29 pp. 6 pls. |
| Date | |
| Source | Merumite (Director Creek, northwestern Guyana, northern South America) 2 |
| Author | James St. John |
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This image was originally posted to Flickr by jsj1771 at https://www.flickr.com/photos/47445767@N05/15185405472. It was reviewed on 10 September 2014 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
|---|---|---|---|---|---|
| current | 00:07, 10 September 2014 | | 1,672 × 1,576 (948 KB) | Tillman | Transferred from Flickr via Flickr2commons |
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