Cleveland Dyke from Cliff Rigg Quarry, Gt. Ayton, North Yorkshire. Photograph of a thin section in plane polarised light opaque minerals of iron oxides and cryptocrystalline mesostasis are apparent.

The same thin section (almost) under cross polarised light. The Cleveland Dyke is classed as a basaltic andesite. It is a porphyritic rock with small (1-2mm) phenocrysts of plagioclase feldspar. The groundmass is seen to consist of laths of plagioclase (grey-black interferrence colours and the pyroxene, augite (blue, red & orange interference colours). The bottom left shows two feldspar phenocrysts, the one on the far left, with complex twinning, being 1.5mm in length (north to south).

The photo on the left is a polished section of Redcar Mudstone Formation taken from within a few feet of the dyke contact. Normally it would be a dark gray shale or mudstone. However it has been thermally altered resulting in the "spotting" as well as induration. There does not appear to have been any detailed published analysis of the spots, but it is thought that they could be the result of coagulation of the hydrocarbon content within the mudstone.

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