| P number: | P524229 |
|---|---|
| Caption: | Photomicrograph of felsic porphyrite. Light: PPL, Magnification x 2. 850 feet at 126 degrees from Cougie, Glen Affric, Invernessshire. |
| Description: | The image is a photomicrograph of a thin section of a felsic porphyrite, containing large phenocrysts of clear feldspar within a fine-grained granular matrix of quartz and feldspar with abundant small flakes of dark-coloured biotite mica. British Geological Survey Petrology Collection sample number S 56759. Light: PPL, Magnification x 2. Light: PPL, Magnification x 2. The term porphyrite has long been used by petrologists for a rock which is more correctly called a porphyritic microdiorite. Some of the porphyrites surrounding the Criffel-Dalbeattie granite in south-west Scotland consist of a devitrified glassy matrix in which the abundant and relatively large phenocrysts are embedded. Most of these rocks are intrusive in origin. The felsic porphyrites are a set of minor intrusions associated with the Caledonian Orogeny, they are late- to post-tectonic. They are mostly porphyritic microgranites with phenocrysts of oscillatory-zoned albite-oligoclase, biotite and in places hornblende set in a granoblastic fine-grained groundmass of quartz, potash feldspar and acid plagioclase in equal proportions. They are commonly schistose having been deformed and recrystallized to produce amphibolite or greenschist-facies mineral assemblages. |
| Date taken: | Wed Jan 01 00:00:00 GMT 2003 |
| Photographer: | Hyslop, E.K. |
| Copyright statement: | NERC |
| X longitude/easting: | 224400 |
| Y latitude/northing: | 821000 |
| Coordinate reference system, ESPG code: | 27700 (OSGB 1936 / British National Grid) |
| Orientation: | Landscape |
| Size: | 217.48 KB; 1000 x 667 pixels; 85 x 56 mm (print at 300 DPI); 265 x 176 mm (screen at 96 DPI); |
| Average Rating: | Not yet rated |
| Categories: | Unsorted Images |
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