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Sample Y-58N260
NavDat sample number 2920 · DACITE
Sample
| Sample ID | Y-58N260 |
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| Rock name | DACITE |
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| Rock type | VOLCANIC |
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| Composition | FELSIC |
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| Material | IGNEOUS |
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| Collected by | Charles J. Vitaliano |
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| Comment | A dark gray porphyritic rock with large phenocrysts of feldspar up to 1 cm and smaller biotite up to 1.5 mm in a glassy groundmass. The visible phenocrysts constitute 60% of the rock. In thin section, the very fresh euhedral plagioclase phenocrysts, zoned An39-44 and fractured, constitutes 25% of the rock, and biotite 15%. Phenocrysts of clear unaltered pyroxene diopside, 11%; augite, 5% equally fresh orthoclase 3%, and quartz 3%, although as large or even larger than the biotite phenocrysts, are not conspicuous in hand specimen against the glassy groundmass. The glassy to cryptocrystalline groundmass, with perlitic fracture, contains clots of fine-grained aggregates of the constituent minerals which may represent broken and engulfed crust of the lava flow. The dates obtained on feldspar and biotite are in excellent agreement, not only with each other, but also with the date of 21.1 m.y. reported by Kistler 1968, p. 255 for a dacite vitrophyre collected about four miles southeast of Goldfield Henry Cornwall, written communication. 1971. Kistler's dacite vitrophyre is a welded ash flow tuff; Y-58N260, on the other hand, is distinctly a flow. Nevertheless the field relations and the similarity in composition, as reflected in the petrography, leave no room for doubt that these are merely two phases of the same or closely related volcanic units. |
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Location
| Latitude | 37.8556 |
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| Longitude | -117.14 |
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| Location | Esmeralda County, NV |
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| State / province | Nevada |
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| Volcanic field | Goldfield-Tonopah region, West-Central Nevada |
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| Location comment | Dacite vitrophyre; along primitive road leading from Goldfield to Mud Lake, 2 mi E of Mud Lake |
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Age
| Age (Ma) | Error | Min | Max | Geologic age | Dated by |
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| 22.4 |
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22.1 |
22.7 |
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Analyses
No chemical analyses are stored for this sample.
