Geology 307: Igneous and Metamorphic Petrology (Spring 2015)
Item set
- Title
- Geology 307: Igneous and Metamorphic Petrology (Spring 2015)
- Creator
- Tamara Carley
- Date Created
- 22 January 2015
Items
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MACROSCOPIC: A dark gray medium grained somewhat gneissoid rock consisting of black hornblende, glassy plagioclase, with occasional yellow brown grains of sphere/ MICROSCOPIC: Green hornblende, the dominant species contributes to a moderately well-developed gneissoid foliation in subparallel subhedra, partly replated by biotite, in both anhedral patches and euhedral tablets. The medium plagioclasae in anhedral, slightly zoned gradationally and locally has central parts sericitized. Large sphene euhedra form a conspicuous accessory. Other are epidote, rare allanite, apatite and magnetite. -
Grey Nepheline-Syenite -
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Collection: Lafayette College Sample number: R1826 (Ward's Natural Science Establishment, Inc.) Location: N.W. of Helena, Montana Rock: Dacite Prominent minerals: Contains plagioclase, biotite, amphiboles, pyroxenes, quartz. Type: Felsic/intermediate extrusive igneous rock. Description of hand sample: Porphyritic rock containing gray, white and black grains. White grains appear to be larger than the others, and gray grains mostly make up the matrix. Dark grains are small and not as abundant. Description of thin section: A large amount of glass is present in the rock, indicated by total extinction in XPL. Plagioclase feldspar is also abundant throughout, as indicated by twinning and low birefringence. Small biotite grains are brown and display slight color changes as the stage is rotated. A small amount of pyroxenes and amphiboles are present, indicated by their characteristic cleavage. Some quartz is present, indicated by low birefringence and undulose extinction. Potential history: Dacite is an extrusive felsic/intermediate rock. The rock photographed likely resulted as a silicic magma started to cool gradually (forming the phenocrysts) before being rapidly exploded leading to the creation of a fine matrix with glassy components. -
Basalt -
Gray fine-grained hornblende andesite -
Ultramafic, aphanitic, augite-labradorite basalt -
Gray Porphyritic Hornblende Andesite -
Coarse-Grained Biotite-Hornblende Granite -
Phaneritic Olivine Dunite -
Part of the Carley Iceland research collection. Small, homogeneous felsic intrusion on the southwestern coast of the Snaefellsness Peninsula. Collected 11 June 2011. Zircon trace element and oxygen isotope data published in Carley et al. 2014 (Iceland-Hadean, EPSL).