File:Stichtitic serpentinite (Dundas Ultramafic Complex, Cambrian; Stichtite Hill, western Tasmania) 2 (49146942017).jpg
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Stichtitic serpentinite from Tasmania. (TM 4328, Colorado School of Mines Geology Museum, Golden, Colorado, USA) Greenish = serpentine Purplish = stichtite Tiny black spots within stichtite masses = chromite Ophiolites are fragments of oceanic lithosphere (basaltic crust + uppermost mantle) that have been metamorphosed and plastered onto the edges of continental lithospheric plates by obduction (the opposite of subduction). This ophiolite rock is a serpentinite with purplish- to lilac-colored masses of stichtite, a rare hydrous magnesium chromium hydroxy-carbonate mineral (Mg6Cr2CO3(OH)16·4H2O). The rock comes from Stichtite Hill in western Tasmania, the type locality for stichtite. The host rocks are chromitic-magnetitic serpentinites of the Dundas Ultramafic Complex, a Cambrian-aged ophiolite that's been cut up by thrust faults. Before metamorphism, the serpentinite was a chromitic dunite (as were several of the rocks in this ophiolites photo album). Dunite is an ultramafic, intrusive igneous rock (peridotite) with >90% olivine. The origin of stichtite is not yet completely resolved. The stichtite masses have tiny black specks of chromite, which was a component of the original dunite. What's seems to be clear is that the stichtite is derived from the chromite by hydrothermal metamorphism. The details of the alteration process are still discussed in the literature. The timing of stichtite formation is also unclear. Several orogenic and thermal events affected the rocks of western Tasmania during the Devonian, Jurassic, Cretaceous, and Cenozoic. Stichtite formation could have accompanied any one of those events. Stichtite info. synthesized from: Ashwal & Cairncross (1997) - Mineralogy and origin of stichtite in chromite-bearing serpentinites. Contributions to Mineralogy and Petrology 127: 75-86. Bottrill & Graham (2006) - The nature and origin of stichtite from western Tasmania. Abstracts of the Australian Earth Sciences Convention 2006. 3 pp. |
| Date | |
| Source | Stichtitic serpentinite (Dundas Ultramafic Complex, Cambrian; Stichtite Hill, western Tasmania) 2 |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/49146942017. It was reviewed on 30 November 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 17:09, 30 November 2019 | | 2,943 × 1,757 (5.73 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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