This specimen is an example of a mineral that formed in an epithermal environment.
Hydrothermal fluids crystallizing at shallow depths of only 1,000 to 2,000 feet and at temperatures of only 100°C to 200°C develop an epithermal deposit. Minerals typical of epithermal deposits include the sulfantimonides and sulfarsenides of silver, the gold and gold-silver tellurides, and native gold. Stibite and cinnabar, important sources of antimony and mercury respectively, are minerals common to epithermal deposits. Especially rich and valuable concentrations of native gold and silver are often deposited under epithermal conditions. These may develop with other epithermal minerals that have little commercial importance.
Lake Superior, Michigan