Calcite.  Ton Mawr quarry.

Calcite. Ton Mawr quarry.

Another example of calcite crystals, again from one of the limestone quarries of South Wales. Calcite is Calcium carbonate CaCO3, and these crystals are of the variety known as "nailhead". The colour is cream with a hint of orange, and no other minerals present.  I collected this specimen many years ago from Ton Mawr quarry, in South Wales.