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obsidian

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Journal Article
Published: 01 June 2017
Italian Journal of Geosciences (2017) 136 (2): 238-262.
... as caementia . The grey-black volcanic rocks are glasses with characteristics more near to obsidian and less to natural pozzolan normally used in the Roman period. To identify the provenance of these glasses, a geochemical comparison between the samples taken from the theatre mortars and the volcanic outcrops...
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Journal Article
Journal: Geology
Published: 01 February 2017
Geology (2017) 45 (2): 183-186.
... fragments. We show that individual obsidian pyroclasts from Mono Craters, California (USA), are heterogeneous in dissolved H 2 O and CO 2 , suggesting that clasts are assembled from juvenile melt and rewelded ash during magma ascent. This is in contrast to the conventional view that clasts are chemically...
Journal Article
Journal: Geology
Published: 01 July 2015
Geology (2015) 43 (7): 647-650.
...Kenneth S. Befus; James Watkins; James E. Gardner; Dominique Richard; Kevin M. Befus; Nathan R. Miller; Donald B. Dingwell Abstract Spherulites in rhyolitic obsidian provide a record of the thermal history of their host lava during the interval of spherulite growth. We use trace element...
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Journal Article
Published: 01 June 2015
European Journal of Mineralogy (2015) 27 (3): 353-363.
..., minor and trace elements. Two main groups of natron-based silica–lime glass were identified, as well as one sample of obsidian (from Lipari Island). The majority of the samples (20) are High Iron, Manganese and Titanium (HIMT) glass. Specifically, most of them (18) can be classified as HIMT1, with only...
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Journal Article
Published: 01 April 2015
American Mineralogist (2015) 100 (4): 774-786.
...Amy G. Ryan; James K. Russell; Alexander R.L. Nichols; Kai-Uwe Hess; Lucy A. Porritt Abstract We present a suite of 36 high-temperature (900–1100 °C) experiments performed on 10 × 10 mm unjacketed cores of rhyolitic obsidian from Hrafntinnuhryggur, Krafla, Iceland, under atmospheric pressure...
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Journal Article
Published: 01 July 2014
American Mineralogist (2014) 99 (7): 1383-1403.
... material of common granitic composition (Lake County obsidian) reduces the crystallization and melting temperatures by approximately 50–70 and 200 °C, respectively, and promotes the formation of quartz-feldspar graphic and granophyric intergrowths. The presence of Li in the hydrous granitic system lowers...
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Journal Article
Journal: Geology
Published: 01 July 2013
Geology (2013) 41 (7): 779-782.
...Kurt Rademaker; Michael D. Glascock; Bruce Kaiser; David Gibson; Daniel R. Lux; Martin G. Yates Abstract We report results from comprehensive mapping and multi-technique geochemical characterization of obsidian from the Alca source in the Peruvian Andes (15.3°S, 72.7°W), aimed at understanding...
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Journal Article
Journal: Geology
Published: 01 January 2013
Geology (2013) 41 (1): 7-10.
... crystallization ages for two obsidian-bearing lavas: Red Island (the host for the granophyre) and Obsidian Butte, a prehistoric quarry for obsidian that is widely distributed in southern California and northern Mexico archaeological sites. Lavas and granophyre display overlapping zircon crystallization age...
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Journal Article
Journal: Geology
Published: 01 August 2012
Geology (2012) 40 (8): 699-702.
...James M. Watkins; Michael Manga; Donald J. DePaolo Abstract Water concentration profiles around bubbles offer a new kind of geobarometer. We measure H 2 O and CO 2 concentrations in glass adjacent to bubbles in pyroclastic obsidian from Mono Craters, California (United States). H 2 O and CO 2...
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Journal Article
Journal: Geology
Published: 01 January 2011
Geology (2011) 39 (1): 67-70.
...Agustín Cabrera; Roberto F. Weinberg; Heather M.N. Wright; Sergio Zlotnik; Ray A.F. Cas Abstract We present water content transects across a healed fault in pyroclastic obsidian from Lami pumice cone, Lipari, Italy, using synchrotron Fourier transform infrared spectroscopy. Results indicate...
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Journal Article
Published: 01 September 2009
Journal of the Geological Society (2009) 166 (5): 895-904.
... spectrometry (DSC–TGA–MS) and X-ray diffraction (XRD). Samples range from pristine obsidians to strongly perlitized and altered fragmental deposits. Four types of samples are determined to have notable differences in total volatile concentrations: obsidians (0.44–3.04 wt%), perlites (2.15–8.15 wt%), obsidian...
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Journal Article
Published: 01 November 2008
American Mineralogist (2008) 93 (11-12): 1816-1822.
...Jonathan M. Castro; Pierre Beck; Hugh Tuffen; Alexander R.L. Nichols; Donald B. Dingwell; Michael C. Martin Abstract We determined the kinetics of spherulite growth in obsidians from Krafla volcano, Iceland. We measured water concentration profiles around spherulites in obsidian by synchrotron...
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Journal Article
Journal: Geology
Published: 01 April 2008
Geology (2008) 36 (4): 279-282.
... eruptions occurred from three aligned vents, reflecting an underlying, segmented feeder dike ( Fink, 1985 ). These events produced fall deposits composed of white pumice lapilli (~95%) and juvenile pyroclastic obsidian and lithic fragments (~2%–5%). Pyroclastic flows occurred after column-producing...
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Journal Article
Journal: GSA Bulletin
Published: 01 November 2007
GSA Bulletin (2007) 119 (11-12): 1337-1347.
..., and is composed of fine-grained, light-gray, porphyritic rhyolite that grades to coarse, crystalline rhyolite in the core of the dome. The intrusion is surrounded by ash and obsidian deposits exposed both east and west of the rhyolite dome. Interbedded with the ash and obsidian (Fig. 2A) are several megabreccia...
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Journal Article
Published: 01 June 2007
The Canadian Mineralogist (2007) 45 (3): 551-557.
...Chi Ma; George R. Rossman; James A. Miller 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...
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Journal Article
Journal: Geology
Published: 01 July 2006
Geology (2006) 34 (7): 517-520.
...Lawrence M. Anovitz; Lee R. Riciputi; David R. Cole; Mostafa Fayek; J. Michael Elam Abstract The natural hydration of obsidian was first proposed as a dating technique for young geological and archaeological specimens by Friedman and Smith (1960) , who noted that the thickness of the hydrated layer...
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Journal Article
Published: 01 May 2004
European Journal of Mineralogy (2004) 16 (3): 419-429.
...Pasquale ACQUAFREDDA; Antonio PAGLIONICO Abstract SEM-EDS non-destructive analysis allows the source discrimination of the various microphenocrysts in obsidian rocks of the Mediterranean. Samples of six Mediterranean sources, Monte Arci (Sardinia), Palmarola, Lipari, Pantelleria, Gyali and Melos...
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Journal Article
Journal: Geology
Published: 01 April 2004
Geology (2004) 32 (4): 349-352.
...A.C. Rust; K.V. Cashman; P.J. Wallace Abstract Obsidian pyroclasts, a common component of rhyolitic tephra, preserve a range of volatile contents, which has been used to infer syneruptive conditions of magmatic degassing. Here we show that the textures of obsidian pyroclasts provide information...
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Journal Article
Journal: Geology
Published: 01 December 2003
Geology (2003) 31 (12): 1089-1092.
... is a rechargeable trigger mechanism for hybrid seismicity and show that the time scale of the process and the fractures formed by it are consistent with the repeat time and magnitude of hybrid earthquakes during silicic eruptions. The RFH process may also form the flow banding that is nearly ubiquitous in obsidian...
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Journal Article
Published: 01 February 2001
The Canadian Mineralogist (2001) 39 (1): 57-71.
...Chi Ma; Jennifer Gresh; George R. Rossman; Gene C. Ulmer; Edward P. Vicenzi Abstract Samples of Mexican obsidian that exhibit either “sheen” or “rainbow” optical properties were examined with a combination of EMP, SEM, TEM, as well as visible and IR spectroscopy. Electron-microprobe analyses...
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