| P number: | P521329 |
|---|---|
| Caption: | Rock specimen of diorite. Garabal Hill, head of Loch Lomond, Glen Falloch, Dumbartonshire, Scotland. |
| Description: | The sample is an excellent example of a diorite, showing a uniform coarse-grained crystalline texture, composed of dark biotite and hornblende, within a matrix of pale grey plagioclase feldspar. British Geological Survey Petrology Collection sample number EMC2058. A diorite is a coarse-grained igneous rock with an 'intermediate' composition. With increasing quartz they grade into granodiorites, and when the plagioclase becomes more calcium-rich they grade into gabbros. The Garabal-Hill Glen Fyne Complex is classed as one of the post-tectonic granitic intrusions of the Caledonian Orogeny and is dated at 406 Ma (Devonian in age). It is divided into two parts by the Kinglas-Garabal fault. To the north-west of the fault lies the main part of the body, which comprises mostly granodiorite with K-feldspar megacrysts, with a subsidiary non-porphyritic granodiorite (Nockolds, 1941). Along its south-east margin, adjacent to the fault, the granodiorite has a contact with a small body of hypersthene-gabbro containing a minor ultramafic phase (augite-peridotite). |
| Date taken: | Sun Dec 01 00:00:00 GMT 2002 |
| Photographer: | McTaggart, F.I. |
| Associate: | T.S. Bain |
| Copyright statement: | NERC |
| Additional information: | EMC2058 |
| Orientation: | Landscape |
| Size: | 283.71 KB; 1000 x 775 pixels; 85 x 66 mm (print at 300 DPI); 265 x 205 mm (screen at 96 DPI); |
| Average Rating: | Not yet rated |
| Categories: | Best of BGS Images/ Geological structures |
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