Detailed Description

A group of bournonite “cogwheel” twins featuring one larger twin. The larger twin exhibits the approximately cruciform symmetry shown in textbooks for some cogwheel twins. The crystals are sharp and well-defined. The prism faces are highly lustrous, while the terminations have good lustre. In excellent condition, one tiny nick on a small crystal and one chip out of a small crystal at the far lower left edge. These are absolutely classic bournonite crystal forms – a great specimen!

About These Bolivian Bournonites

These bournonite crystals are from the Viboras Mine, Machacamarca District, Potosí, Bolivia. The locality has produced excellent bournonite specimens over the years, but the finds are have been sporadic, often years apart. The nature of the bournonite has varied from one find to the next, and some of the bournonite has been of modest lustre, sometimes dull, and of varying sharpness/definition. This latest find has produced sharp, lustrous bournonite crystals of the finest quality, exhibiting the classic “cogwheel” twinning.