Calcite, CaCO3 (Calcium Carbonate), is one of the commonest minerals, being the main constituent of limestone. Calcite is often fluorescent, a small amount of Managnese is enough to make it glow red under UV light. The mineral will bubble in acid distinguishing it from many similar species, even other carbonates which do not dissolve so easily in cold acids.

Description: A sizeable brown matrix containing a large indentation. This is lined by a mixture of clear, cubic Fluorite crystals and a crust of white, crystalline Calcite. Some of the Fluorite crystals are twinned. The Calcite crust extends to some of the Fluorite crystals so that only the upper surface shows through. An interesting effect rather like a dusting of icing sugar. The fluorite is moderately fluorescent, the blue providing a nice contrast against the white of the Calcite.

Location: Heights Quarry, Eastgate, Weardale, Co Durham, England.