| P number: | P521359 |
|---|---|
| Caption: | Rock specimen of spherulitic pitchstone. Corrygills shore, east-south-east of Brodick, Arran, Buteshire, Scotland. |
| Description: | The sample is a striking pale-coloured banded igneous rock composed of thin layers of 'acidic' volcanic lava, that is rich in quartz and feldspar. The magma has been erupted with such speed that it has very rapidly chilled to give a glassy rock (known as pitchstone) which has over time recrystallized (or devitrified) to a more crystalline structure. The white specks in certain bands are small spherules where minerals have grown during this devitrification process. The pale orange staining is due to later movement of iron oxide through the rock. British Geological Survey Petrology Collection sample number EMC1993. The term spherulitic is used to describe a particular texture, usually in an igneous rock, where crystals of a needle-like form occur in globular clusters with the crystals radiating outwards. They result from the crystallization or 'devitrification' of glassy volcanic rocks such as rhyolite or pitchstone. Tertiary quartz-porphyry and pitchstone sills are widely distributed throughout Arran. Quartz-porphyry sills are usually massive and the pitchstones relatively thin. |
| Date taken: | Sun Dec 01 00:00:00 GMT 2002 |
| Photographer: | McTaggart, F.I. |
| Associate: | T.S. Bain |
| Copyright statement: | NERC |
| Additional information: | EMC1993 |
| Orientation: | Landscape |
| Size: | 223.78 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: | Unsorted Images |
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