The image shows part of a thin section of black sandstone viewed under crossed-polarized light. The rock is dominated by quartz and feldspar which are various shades of grey, from white to black. The specimen is of Carboniferous age. British Geological Survey Petrology Collection sample number ED 7591.
Some of the sandstone at the Ravelston Quarry is black in colour because of the presence of hydrocarbon which infills pore spaces and coats many of the quartz and feldspar sand grains. The hydrocarbon may have flowed into the porous sandstone as a result of heating from the nearby Corstorphine Hill igneous sill.
The Ravelston Sandstone is part of the Carboniferous Lower Oil shale Group. It is located on the south-west side of the Granton Dome. It is approximately 125 feet thick at its maximum, and was worked mainly in quarries on Corstorphine Hill in western Edinburgh. It lies stratigraphically above the Craigleith Sandstone within the Gullane Formation. Early quarrying of sandstone from this or a higher stratigraphical level may have taken place in and around Leith.
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