The calcite is polymorph of Aragonite.
It is a very widespread stone, however, because of its low hardness, it is a very difficult to cut. A gem cut calcite is a rare gemstone for collectors.
Calcite physical properties gives it an original effect: the duplication. If you place a line behind the stone and look through it, the line will appear as a double line.
To learn more about the mineralogy of the calcite, see Mindat.org
To see some calcite for sale
See the blue calcite for sale
