My mineral collection part 4, Aragonite

Today I'm going to show you one of the pretties specimens I have collected.
I'm talking about Aragonite, it is one of the most common crystal forms of calcium carbonate CaCO3 ( your ordinary chalk) .

The interesting thing about it is that it is biogenerative and that it is not stable under normal pressure and temperature and undergoes a change in to a more stabile form, calcite.
It can be found in various colours which are caused by impurities, this one is a brown caramel colour.
Enjoy.