3.5" Orange Aragonite on Scalenohedral Calcite - Mexico

This is a gorgeous specimen which features red-orange aragonite that formed after a scalenohedral calcite crystal. The rhombohedral cleavage of the calcite can be seen on what could be considered the underside of the specimen. This mineral association was collected from Chihuahua, Mexico.

Aragonite is one of two common calcium carbonate (CaCO3) minerals: the other is calcite, of which aragonite forms as a pseudomorph. Its crystal lattice differs from calcite, resulting in a different crystal shape. It displays a translucent to white color when pure, and when impure can vary between yellow, green, pink, blue and brown. It typically forms in low-temperature hydrothermal veins, in hot springs, and as precipitates from chemicals in sedimentary rock. It can also form under biological processes: aragonite forms naturally in most mollusk shells, and as the calcareous endoskeleton most corals.

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.
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DETAILS
SPECIES
Aragonite & Calcite
LOCATION
Chihuahua, Mexico
SIZE
3.5 x 3.1"
CATEGORY
ITEM
#127083