Quartz forms in the geodes lining cavities carved out by dissolving dolomitic limestone rock. The length of each crystal prism is usually three or four times its thickness. Its most distinctive feature is a star-shaped alternating colouring running along the principal axis. Occasionally, it alternates with citrine colouring.

For years, this variety of quartz, known as ametrine or bolivianite, aroused suspicion among gemmologists, who refuted its natural origin. This is the only region in the world where ametrine is found. The Ayoreita Mine, whose owner is a Bolivian citizen, extracts and markets several varieties of amethyst quartz and ametrine trough Ayoreita Mining Company.