Published June 2007
| public
Journal Article
Open
The origin of color in "fire" obsidian
- Creators
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Ma, Chi
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Rossman, George R.
- Miller, James A.
Abstract
A variety of obsidian from Glass Buttes, Oregon, known as "fire" obsidian and named for thin layers showing various colors, was investigated with field-emission scanning electron microscopy, X-ray energy-dispersive spectroscopy, electron back-scatter diffraction, and optical spectroscopy methods. Our study reveals that the thin layers mainly consist of concentrated nanometric crystals of magnetite. The thin layers, which have a thickness of 300 to 700 nm, give rise to brilliant colors in reflection. The color is caused by thin-film optical interference, in which the thin layers have a higher calculated index of refraction (1.496 < n < 1.519) than that of the host glass (n = 1.481).
Additional Information
© 2007 Mineralogical Association of Canada. Received January 6, 2006; revised manuscript accepted September 15, 2006. FE–SEM, EDS and EBSD analyses were done at the Caltech GPS analytical facility, which is supported in part by the MRSEC Program of the NSF under DMR–0080065. Additional support was provided to G.R.R. through NSF grant EAR–0337816. A special "thank you" is extended to Nadine and Don Carey, owners of the fire obsidian claim, who granted permission to collect samples. The photos of fire obsidian shown in Figure 1 were supplied by Steve Sayer for this publication.Files
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Additional details
- Eprint ID
- 9084
- Resolver ID
- CaltechAUTHORS:MACcm07
- Created
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2007-10-26Created from EPrint's datestamp field
- Updated
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2020-03-09Created from EPrint's last_modified field
- Caltech groups
- Division of Geological and Planetary Sciences