Aragonite is considered a variety of jade by gemstone craftsman in China. It is composed of aragonite, calcite and siderite, and aragonite and calcite are the main minerals. Aragonite is a polymorph of calcite. Its crystals are prismatic or elongated prismatic but usually in the form of botryoidal, encrusting, stalactitic, fibrous, radiating, coralloid and oolitic aggregates. Aragonite can be white, colourless, grey, light yellow, green, blue, violet, light red or brown. It can be transparent or translucent with a glassy lustre. It has a Mohs hardness of 3.5–4, a specific gravity of 2.94–2.95 and conchoidal fracture. It is mainly found in recently deposited sediment or clay on the seafloor, the sediments of thermal springs and in the fissures and pores of volcanic rocks.