L352 - Dolomitic limestone

Permian

Location

Pale buff coloured, crystalline rock. 
Numerous cavities, thought to have been formed by shrinkage during alteration of primary calcite (CaCO₃) to secondary dolomite (CaMg[CO₃]₂). There is a weak reaction to dilute acid, which suggests that there may be some calcite remaining. 
Colourless crystalline material infilling holes.

Almost entirely made up of very fine grains of dolomite (which tends to show more rhomb shaped crystals than calcite).
Irregular cavities into which well-developed rhomb crystals of dolomite have grown. Note that one should distinguish between the cavities in the rock (with rhombs of dolomite) and those due to the preparation of the sections.

It is thought that this rock was initially made-up of calcite. The alteration from calcite to dolomite, with its consequent increase in specific gravity and decrease in volume, accounts for the formation of the cavities.

dolmitic limestone
dolomite
magnesian limestone