This quartz variety is a real oddity. It consist of smoky quartz crystals,
usually very clear, with dispersed halos of darker spots on the surface.
The color is just on the surface and doesn’t penetrate too deep in the
quartz so the gemstones have to be cut using the quartz face as the base
and watching the spots through the quartz.
The genesis of Dalmatine quartz is very interesting, they are irradiation
halos, caused by a natural irradiation from small radioactive crystals
formed on the face of the quartz crystal. The radioactive crystals was
probably of Uraninite or just Zircon and they have been completely destroyed,
probably by the atomic decay. So now the stone are absolutely radiation
free and there is no ealth risk.
This deposit was furstly found in 2006 in the Gameleira pegmatite near
Medina in northern Minas Gerais.