An interesting example of strong zoning caused by variable iron content came recently from Bahia State in Brazil ... crystals of yellow citrine with small amethyst sectors, which can be described as ...

Almost all of the quartz needed for these components was harvested from natural crystals, mostly from Brazil and the quarries in Arkansas, from which raw slabs were painstakingly cut, polished ...

and quartz, which belong to either the trigonal or the hexagonal crystal system, can show a trapiche-like texture with a hexagonal core and six extended arms when viewed down the c-axis. Four trapiche ...