Properties of truly magmatic epidote
Euhedral phenocrysts of prismatic epidote up to 4mm in length are present (2 modal %) in a sample of porphyritic rhyodacite (69.5% SiO/sub 2/) in the authors undergraduate teaching collection. The sample is believed to be a Tertiary dike-rock from Ward, Boulder County, Colorado. Phenocrysts of corroded quartz, oscillatory-zoned plagioclase (An30-40), kinked and bent biotite, and very pale yellow pleochroic epidote (Fe/(Fe+Al) = 0.21, 2V(-) large, lamellar twinning on (100)) are set in a finely crystalline groundmass of quartz, potash feldspar (Or92) and oligoclase (An26). Rare small euhedral garnets (Al54Pyl3Gr22 Sp8An3) are enclosed in plagioclase and biotite phenocrysts. Some of the epidote prisms have very pale brown allanitic cores, which are oscillatory-zoned and in part embayed. The bulk of the epidote, however, is poor in allanite component. Critical igneous textural features of the allanite-poor epidote are: euhedral form; euhedral oscillatory zoning; clustering of phenocrysts in synneusis relation; and the presence of euhedral inclusions of zircon that apatite. Since phenocrysts constitute only 26 modal % of the rock, crystallization of epidote, in fact, took place relatively early in the rock's cooling history. A description of this rock is provided as a petrographic guide to those using allegedly magmatic epidote in silicic plutonic rocks as an indicator of minimum pressure of crystallization.
- Research Organization:
- Univ. of Washington, Seattle (USA)
- OSTI ID:
- 6611348
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
EPIDOTES
CRYSTALLIZATION
MAGNETIC PROPERTIES
MINERALOGY
PETROGRAPHY
BIOTITE
COLORADO
FELDSPARS
GARNETS
GEOLOGIC HISTORY
QUARTZ
TERTIARY PERIOD
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CALCIUM COMPOUNDS
CALCIUM SILICATES
CENOZOIC ERA
CHALCOGENIDES
FEDERAL REGION VIII
GEOLOGIC AGES
IRON COMPOUNDS
IRON SILICATES
MICA
MINERALS
NORTH AMERICA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
TRANSITION ELEMENT COMPOUNDS
USA
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)