This is a beautiful find out of Argentina, featuring true pink amethyst crystals that formed in association with calcite, from the Choique Mine. It occurs in geodic formations or cavities lined with crystals. This piece is 2.7" wide and the crystals have an excellent dark, pink color and nice terminations.
The material has been analyzed at the California Institute of Technology and was described as "purplish pink amethystine quartz additionally coloured by microscopic hematite particles. They are not rose quartz
or pink quartz as classically defined".
So, it's formed by the same same processes that give amethyst it's purple color, but by definition amethyst is purple not pink. So, we are left with a conundrum of what to call it, but since the majority of people seem to be calling it "pink amethyst" we will stick with that label.
Calcite, CaCO3, is a carbonate mineral and the most stable polymorph of calcium carbonate. The other polymorphs are the minerals aragonite and vaterite. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals. However, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, and prisms. Calcite exhibits several twinning types adding to the variety of observed forms. It may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form.