Hematite

Hematite, also spelled as haematite, is a common iron oxide with the formula Fe2O3 and is widespread in rocks and soils. Hematite crystallizes in the rhombohedral lattice system, and it has the same crystal structure as ilmenite and corundum. Hematite and ilmenite form a complete solid solution at temperatures above 950 °C (1,740 °F).A rare pseudo-scalenohedral crystal habitThree gemmy quartz crystals containing bright rust-red inclusions of hematite, on a field of sparkly black specular hematiteGolden acicular crystals of rutile radiating from a center of platy hematiteCypro-Minoan cylinder seal (left) made from hematite with corresponding impression (right), approximately 14th century BCA cluster of parallel-growth, mirror-bright, metallic-gray hematite blades from BrazilHematite carving, 5 cm (2 in) longHematite, variant specularite (specular hematite), with fine grain shownRed hematite from banded iron formation in WyomingHematite on Mars as found in form of 'blueberries' (named by Nasa)Streak plate, showing that Hematite consistently leaves a rust-red streak. Hematite, also spelled as haematite, is a common iron oxide with the formula Fe2O3 and is widespread in rocks and soils. Hematite crystallizes in the rhombohedral lattice system, and it has the same crystal structure as ilmenite and corundum. Hematite and ilmenite form a complete solid solution at temperatures above 950 °C (1,740 °F). Hematite is colored black to steel or silver-gray, brown to reddish brown, or red. It is mined as the main ore of iron. Varieties include kidney ore, martite (pseudomorphs after magnetite), iron rose and specularite (specular hematite). While the forms of hematite vary, they all have a rust-red streak. Hematite is harder than pure iron, but much more brittle. Maghemite is a hematite- and magnetite-related oxide mineral. 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. The mineral can precipitate out of water and collect in layers at the bottom of a lake, spring, or other standing water. Hematite can also occur without water, however, usually as the result of volcanic activity. Clay-sized hematite crystals can also occur as a secondary mineral formed by weathering processes in soil, and along with other iron oxides or oxyhydroxides such as goethite, is responsible for the red color of many tropical, ancient, or otherwise highly weathered soils. The name hematite is derived from the Greek word for blood αἷμα haima, due to the red coloration found in some varieties of hematite. The color of hematite lends itself to use as a pigment. The English name of the stone is derived from Middle French hématite pierre, which was imported from Latin lapis haematites around the 15th century, which originated from Ancient Greek αἱματίτης λίθος (haimatitēs lithos, 'blood-red stone'). Ochre is a clay that is colored by varying amounts of hematite, varying between 20% and 70%. Red ochre contains unhydrated hematite, whereas yellow ochre contains hydrated hematite (Fe2O3 · H2O). The principal use of ochre is for tinting with a permanent color. The red chalk writing of this mineral was one of the earliest in the history of humans. The powdery mineral was first used 164,000 years ago by the Pinnacle-Point man possibly for social purposes. Hematite residues are also found in graves from 80,000 years ago. Near Rydno in Poland and Lovas in Hungary red chalk mines have been found that are from 5000 BC, belonging to the Linear Pottery culture at the Upper Rhine. Rich deposits of hematite have been found on the island of Elba that have been mined since the time of the Etruscans. Hematite is an antiferromagnetic material below the Morin transition at 250 K (−23 °C), and a canted antiferromagnet or weakly ferromagnetic above the Morin transition and below its Néel temperature at 948 K (675 °C), above which it is paramagnetic.