Hematite

Hematite usually occurs as massive opaque material with a metallic lustre, showing a blood-red colour when cut into thin slices.  However it can also occur as short, black, rhombohedral crystals and may have iridescent surfaces.  Shiny crystals may be called "specular" hematite, a name derived from their traditional use in mirrors.  In the past it was used to protect the wearer from bleeding.