Lugarite

 Geology: the Lugar Sill

Lugarite from the Lugar Sill near Lugar, Ayrshire

Close to the village, and cropping out for a length of about 5 kilometres in a NE-SW direction, is the Lugar Sill, an internationally studied geological feature and a Site of Special Scientific Interest. It has been intruded in several phases (on or close to the Carboniferous-Permian boundary) in molten form (magma) into the local sandstone and then crystallised. The thickness of the igneous rock is estimated at 42-49 m. It extends in a general north-easterly direction from Lugar, 2.5 km beyond the village of Cronberry. Its composition overall is outer teschenite units and a thick core of layered theralite and picrite including lugarite, (a coarse-grained rock consisting of euhedral crystals of titanaugite and kaersutite up to 7cm long with corroded feldspars and ilmenite set in a cloudy greyish base of analcime, nepheline and alteration products). The sill represents a nearby magma source differentiating in situ to give sequentially injected layers of slightly different chemical composition.