Brucite marble, metamorphosed Durness Limestone

Ledmore North quarry

Outcrop

Complex nodular and banded marble, metamorphosed Durness Limestone, Ledmore

Hand specimen

Light grey marble, metamorphosed Durness Limestone, Ledmore

Thin section

Brucite marble, metamorphosed Durness Limestone, Ledmore
Some of the homogeneous light-coloured marbles at Ledmore have this distinctive texture, which reveals that they must have reached extremely high temperatures during contact metamorphism by the syenites. The squarish shapes are made of bundles of flakes of the mineral brucite, which is magnesium hydroxide, and they are set in a matrix of brown calcite These were once cubes of magnesium oxide, formed from the breakdown of the original sedimentary dolomite (calcium magnesium carbonate) at very high temperature.

Plane polarized light. Field of view 2.5 mm across

D.J. Waters, Department of Earth Sciences, May 2003