| P number: | P519816 |
|---|---|
| Caption: | Microscopic sections of slate A at right-angles to the cleavage; B parallel with the cleavage; C strain-slip cleavage, Scotland |
| Description: | Microscopic sections of slate A. at right angles to the cleavage; B parallel with the cleavage; C strain-slip cleavage. The cleavage planes in slate are, in general, at right angles or at a high angle to the direction of the pressure which has led to their formation. The reason for the ready fissility of slates parallel to the cleavage and for their great resistance to forces applied at right angles to the cleavage, is apparent when thin sections of the rock are examined under the microscope. The specimen is of Precambrian, Dalradian age. It is seen in the case of the Ballachulish and Easdale slates that minerals such as quartz occur as little plates with their flat faces all lying in a particular direction, parallel to which certain dark-coloured flaky minerals (mica and some chlorite) are also developed in abundance, A in the diagram. Parallel to this direction the rock splits very readily; at right angles to it, the rock possesses great strength owing to the overlapping effect of the tiny plates of quartz and films of mica, which may be compared to the bonding of bricks in a wall. In the case of the Aberfoyle slates, the quartz grains are not usually flattened, and the fissility of the rock is largely due to the development of flaky minerals, mainly mica. In addition to true cleavage, an aberrant kind of cleavage called strain-slip cleavage is very prevalent. This consists of very closely spaced fracture planes, like miniature faults and can be seen in C. |
| Date taken: | Wed Jan 01 00:00:00 GMT 2003 |
| Photographer: | Bain, T.S. |
| Copyright statement: | NERC |
| Orientation: | Landscape |
| Size: | 142.15 KB; 1000 x 654 pixels; 85 x 55 mm (print at 300 DPI); 265 x 173 mm (screen at 96 DPI); |
| Average Rating: | Not yet rated |
| Categories: | Unsorted Images |
Loading...
Loading...
Reviews
There is currently no feedback