Labradorite.
It is a feldspar (30-50% Albite - 50-70% Anorthite).
It is named after the Labrador Peninsula, Canada. Where it was discovered.
It can present a type of iridescence called Labradorescence.
The cause of this optical phenomenon is due to the lamellar structure caused by a dissolution process due to a miscibility gap.
This effect is visible when the laminar separation is between 128 and 252nm.
Another requirement for lamellar separation is cooling, which is necessary to allow Ca, Na, Si, and Al ions to disperse and produce lamellar separation.