Aragonite

ARAGONITE

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Aragonite pseudomorphs (dolomite) in calcite, Monroe, Washington, USA

Almost all Aragonite crystals are twinned growths of three individual crystals that form pseudohexagonal trillings . Therefore, although Aragonite crystallizes in the orthorhombic system, virtually all its crystals are hexagonal shaped. The trillings can be noted from the basal striations on each of the three individual crystals running in different directions, causing a hexagonal crystal to have three striation directions on each base.

Aragonite frequently contains sand inclusions, which give a specimen a brown color. It forms in many environments, but a particularly interesting one is its formation from deposition of hot, mineral-rich springs. The water releases the calcium it contains upon reaching the air, and forms mounds and thick crusts around the springs. When these deposited mounds and crusts are banded, they are sometimes carved and termed "Onyx Marble", "Suisan Marble", "California Onyx", or "Mexican Onyx".

Aragonite is the main component of many organic substances, such as pearl and coral. The iridescent surface of pearl and mother-of-pearl is a layer of Aragonite secreted by mollusks and related invertebrates.

aragonite from Morocco (unpseudomorphed) - demonstrating the brown colour created by sand

Hardness: 3.-4. Other characteristics.