English: Thin section of Hillhouse Gabbro from near Dundonald in Scotland.

A photomicrograph of a petrographic section of the local rock, an analcime gabbro of Carboniferous age. The rock slice has been cut and lapped to 30 micrometres thickness, then photographed by a high-resolution camera attached to a polarising microscope. The false colours are caused by retardation of the polarised light which travels at different speed depending upon its alignment with the crystal axes. Perfectly isotropic materials are completely black, as are crystals whose axes align with the planes of polarisation. The colours enable geologists to identify the minerals of the rock - here pyroxene and olivine are bright, while plagioclase feldspar is humbug-striped. The length of the large, blue crystal is around 1.6mm.

The section was prepared by the photographer in his own workshop/kitchen from material collected from Hillhouse Quarry (latitude 55:34.4379N, longitude 4:36.9120W).