A variation of schist, this particular specimen was collected by staff from Aberfeldy, Scotland. It comes from the Ben Eagach formation and is part of the famous Pre-Cambrian Dalradian series. It has a smooth, almost greasy texture when one runs ones fingers across the surface. Samples are black, dark grey or blue in colour. The mineral composition of mica and graphite give it a metallic lustre and shine. The graphite is thought to have been derived from the reduction of carbon in organic rich sediments during metamorphic processes. These rock specimens are available in 3 different sizes and will come supplied in labelled card trays.