2.5" Gemmy Cassiterite Crystals On Quartz - Viloco Mine, Bolivia

This is a beautiful, 2.5" wide association of gemmy, black-brown cassiterite crystals, bladed siderite, grey arsenopyrite crystals, pyrite, quartz and tiny tourmaline crystals. It comes from the Viloco (Araca) Mine in the La Paz Department of Bolivia, a site renown for its high quality cassiterite specimens.

The Viloco Mine (also referred to as Araca Mine) is a tin mine in the La Paz Department of Bolivia that produces high quality mineral specimens, most notably cassiterite. It is the only mine in Bolivia that produces transparent, gem quality cassiterite for faceting. These cassiterite crystals are commonly found in peribatholithic cassiterite veins.

Cassiterite, also known as tinstone, is the primary ore of tin. When pure, cassiterite will be colorless, but in most cases impurities will result in brown or black crystals. It is typically found in hydrothermal veins and pegmatites in regions of granite intrusion. In the appropriate environment, it can also precipitate from volcanic gas.

Chemical Formula: SnO2 (tin oxide)

Arsenopyrite is an iron arsenic sulfide with the chemical formula FeAsS. It is the most common arsenic-bearing mineral and is its principal ore, and can be found in igneous, metamorphic and sedimentary rock. Crystals can be found as prismatic, twinned, columnar, elongated and massive formations within veins and are found in locations all around the world. Depending on minerals present during formation, the iron in arsenopyrite can be replaced by cobalt, forming cobaltite.

Arsenopyrite contains a significant amount of poisonous arsenic, making it somewhat toxic. Washing hands following handling is recommended.
Cassiterite, Siderite, Arsenopyrite, Pyrite, Tourmaline & Quartz
Viloco (Araca) Mine, Loayza Province, La Paz Department, Bolivia
Entire specimen: 2.5 x 1.7", largest cassiterite crystal: .6" wide