This is an irregular piece of Hematite which has been polished and fitted to be used as a keychain. Pieces may differ slightly from the examples above.
Hematite also spelled Haematite is a mineral, colored black to steel or silver-gray, brown to reddish brown, or red. It is mined as the main ore of iron.
Huge deposits of hematite are found in banded iron formations. Gray hematite is typically found in places that can have still standing water or mineral hot springs, such as those in Yellowstone National Park in North America. Hematite can also occur without water, however, usually as the result of volcanic activity.