Calcite and Mottramite

Calcite

Calcite forms crystals of very different shapes: rhombohedral, prismatic, tabular, etc. There are also cases in which it occurs as granular, lamellar, parallel or columnar aggregates. Often colourless or whitish, calcite can also form crystals of various colours: pinkish, yellow, brown or green. It has a vitreous to pearly lustre, with semi-hard, light crystals, soluble in cold hydrochloric acid.

Calcite is typically sedimentary in formation, of chemical or organic formation. It can sometimes also have a metamorphic origin or form in hydrothermal veins, and rarely a magmatic one.

It is used in the chemical, metallurgical, in building and in sculpture.

Mottramite

Mottramite, very similar to descloizite, forms pyramidal crystals, tabular or prismatic and, in other cases, crusts and compact masses with fibrous structures and botryoidal surfaces. The colour varies from orange-red to brownish black, but it can also be green in tone.

It is affected by acids and is easily soluble. It forms in the oxidation zones of lead, zinc and copper.

The most common use of these minerals relates to the extraction of vanadium.