Haematite, so named from the Greek haima, blood, from its red streak, is the mineral sesquioxide of iron, containing, when pure, 70 per cent. of iron and 30 per cent. oxygen. When crystalline it belongs to the Rhombohedral system, occurring in rhombohedra and tabular crystals of an iron-black or steel-grey colour, sometimes with a splendent metallic lustre, when it is known as specular iron-ore, such specimens from Elba having been employed by the Romans as hand-mirrors (specula). Its hardness is 5.5 to 6.5, and its specific gravity 4.5 to 5.3. In very thin plates it appears red by transmitted light, and it has a cherry-red streak. In an earthy condition it is known as red ochre or reddle, and is used as a paint in crayons and in polishing glass. Haematite also occurs commonly in mammillated masses with a radiating internal structure, known as kidney-iron-ore. It is sometimes magnetic. Haematite is one of the chief iron-ores. It occurs, replacing calcite, in pockets and fissure-lodes, in the Carboniferous Limestone, in Furness. and to a less extent in Cumberland, South Wales, Devon, and Cornwall. It is imported from Spain. Pilot Knob, Missouri, is a hill 700 feet high, almost entirely haematite, and a large part of Gellivard in the north of Sweden is similarly made up of this ore. It occurs in lavas at Vesuvius and Ascension.