Aragonite penetrations twins from Mexico. These are examples of psuedohexagonal crystals.
Looking down the "C" axis of the crystals
Aragonite as a cave deposit known as flos ferri, which is an arborescent variety.
CHEMISTRY CaCO3 Calcium carbonate
CRYSTALLOGRAPHY Orthorhombic
CRYSTAL GROWTH AND HABITS Aragonite is dipyramidal, commonly acicular pyramidal, tabular and psuedohexagonal penetration twins.
COLOR AND OTHER OPTICAL PROPERTIES Aragonite can be colorless but is very often white to brown with variations of color in the specimen. It is transparent to translucent.
HARDNESS 3.5 - 4
SPECIFIC GRAVITY 2.9 - 3.0
LUSTER Vitreous
STREAK White
BREAKABILITY Aragonite has subconchoidal fracture and brittle.
OCCURRENCE Aragonite is not as common as its polymorph calcite and is found around hot springs. The nacreous layers of many aquatic mollusks is aragonite. Aragonite also forms as precipitates in caves forming "flos ferri" or sometimes called "cave frost".
ASSOCIATED MINERALS Calcite, Gypsum