Iridium, at a calculated density of 22.65 grams per cubic centimeter, is probably the densest element known to man. Minerals like chengdeite are alloys with metallic bonds that are very similar to the more pure metallic elements and are thus classified as elements. Chengdeite is very rare and new to the mineral world. It is named for Chengde County, China from where it was discovered in placer deposits in just the early 1990's. Since then it has been found as a trace mineral in chromite rich ultra-mafic igneous deposits.
Color is black.
Luster is metallic. Specimens are opaque. Cleavage is absent. Fracture is hackly. Streak is black.