The mines near Tarazout, Sidi Rahal, Morocco have produced these very mysterious, beautiful and rare quartz perimorph geodes for the past 30 years. For many years they were referred to has psuedomorphs or quartz after other minerals, but they are perimorphs. Perimorphs differ from Pseudomorphs because they do not replace the earlier mineral but rather form a crust on top of it. In this case it's quartz/amethyst over an undetermined earlier mineral which has dissolved away. They are found within a hard basalt, and contain very unique forms which has sometimes earned them the name "stalactitic quartz geodes".