An oval cabochon hematite stone set in sterling silver.

Hematite is one of the most abundant minerals on Earth's surface and in the shallow crust. It is an iron oxide. It's metallic graphite color, its name comes from about 300-325 BCE by Theophrastus from the Greek ("aematitis lithos") for "blood stone". 
It is possibly the first mineral ever named ending with a "-ite" suffix.