Dolerite, Judd's Dyke No. 1 (Hunternian Museum, rock number AH4471)

This is the marginal part of this composite intrusion. It consists of colourless elongate crystals of plagioclase, greyish clinopyroxene (probably augite), and a little magnetite.

Between crossed polars, the plagioclase shows typical low order grey and white birefringence colours, and striped "lamellar" twinning is visible in places. The clinopyroxene shows moderate yellow and red to blue colours.

Courtesy of Dr John Faithful