Hematite

Hematite Rose

Hematite Rose

Hematite has several varieties, each with their own unique names.

Hematite Rose is a circular arrangement of bladed crystals giving the appearance of the flower of a rose.

Kidney Ore is the massive botryoidal form and gives the appearance of lumpy kidney-like masses.

Tiger Iron

Tiger Iron is a sedimentary deposit of approximately 2.2 billion years old that consists of alternating layers of silver gray hematite and red jasper, chert or even tiger eye quartz.

Specularite is a micaceous or flaky stone that is sparkling silver gray and sometimes used as an ornamental stone.

Oolitic Hematite is a sedimentary formation that has a reddish brown color and an earthy luster and is composed of small rounded grains.

Oolitic Hematite

Hematite is an important ore of iron and its blood red color (in the powdered form) lends itself well to use as a pigment.  Crystals of Hematite are considered rare and are sought after by collectors as are fine Kidney Ore specimens.

Healing properties of Hematite

Hematite stimulates iron absorption in the small intestine, which in turn improves oxygen supply to the body. It can be in direct contact with the skin, but results in inflammation for some people, so test it carefully on yourself before use.

Physical Characteristics:  Color is steel or silver gray to black in some forms and red to brown in earthy forms. Sometimes tarnished with iridescent colors when in a hydrated form (called Turgite).

Luster is metallic or dull in earthy and oolitic forms.

Transparency: Crystals are opaque.

Crystal System is trigonal; bar 3 2/m

Crystal Habits include tabular crystals of varying thickness sometimes twinned, micaceous (specular), botryoidal and massive. also earthy or oolitic.

Cleavage is absent. However, there is a parting on two planes.

Fracture is uneven.

Hardness is 5 - 6

Specific Gravity is 5.3 (slightly above average for metallic minerals)

Streak is blood red to brownish red for earthy forms.

Associated Minerals include jasper (a variety of quartz) in banded iron formations (BIF or Tiger Iron), dipyramidal quartz, rutile, and pyrite among others.

Notable Occurrences especially nice specimens come from England, Mexico, Brazil, Australia and the Lake Superior region.

Best Field Indicators are crystal habit, streak and hardness.

Hematite, also spelled as haematite, is the mineral form of iron(III) oxide (Fe2O3), one of several iron oxides. Hematite crystallizes in the rhombohedral 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.

Hematite is a mineral, 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. Grey hematite is typically found in places where there has been standing water or mineral hot springs, such as those in Yellowstone National Park in the United States. 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.

Etymology and history

Close-up of hematitic banded iron formation specimen from Upper Michigan. Scale bar is 5.0 mm.

Ochre is a clay that is colored by varying amounts of hematite, varying between 20% and 70%.[3] 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.[3]The name hematite is derived from the Greek word for blood αἷμα aima because hematite can be red, as in rouge, a powdered form of hematite. The color of hematite lends it well in use as a pigment. The English name of the stone is derived from Middle French: Hématite Pierre, which was imported from Latin: Lapis Hæmatites, which originated fromAncient Greek: αἱματίτης λίθος (haimatitēs lithos, “blood-red stone”).

The red chalk winning of this mineral was one of the earliest in history of mankind. The powdery mineral was first used 164,000 years ago by the Pinnacle-Point man obviously for social differentiation.[4] Hematite residues are also found in old graveyards from 80,000 years ago. Near Rydno in Poland and Lovas in Hungary, palaeolitic 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 till the time of the Etruscans.

Jewelry

Hematite's popularity in jewelry was at its highest in Europe during the Victorian era, and has since seen a strong resurgence in North America, especially in the western United States. Certain types of hematite or iron oxide rich clay, especially Armenian bole has been used in gilding. Hematite is also used in art such as intaglio engraved gems. Hematine is a synthetic material sold as magnetic hematite. 

Hematite is sometimes used in jewelry, either as black reflective stones or as a jewelry piece itself (such as a ring). Some jewelry is marketed as "magnetic hematite". I believe that is more likely another iron oxide, magnetite. Almost all hematite jewelry is made of imitation hematite beads. It is sometimes called hematine, but there is no requirement to say that hematite jewelry is actually imitation. In fact, many jewelry makers do not even know it is artificial.

Magnetism

crystal structure of hematite

Hematite is an antiferromagnetic material below the Morin transition at 250 K, and a canted antiferromagnet or weakly ferromagnetic above the Morin transition and below its Néel temperature at 948 K, above which it is paramagnetic.

The magnetic structure of a-hematite was the subject of considerable discussion and debate in the 1950s because it appeared to be ferromagnetic with a Curie temperature of around 1000 K, but with an extremely tiny moment (0.002 µB). Adding to the surprise was a transition with a decrease in temperature at around 260 K to a phase with no net magnetic moment. It was shown that the system is essentially antiferromagnetic but that the low symmetry of the cation sites allows spin–orbit coupling to cause canting of the moments when they are in the plane perpendicular to the c axis. The disappearance of the moment with a decrease in temperature at 260 K is caused by a change in the anisotropy which causes the moments to align along the c axis. In this configuration, spin canting does not reduce the energy.[6][7]

Hematite is part of a complex solid solution oxyhydroxide system having various degrees of water, hydroxyl group, and vacancy substitutions that affect the mineral's magnetic and crystal chemical properties.[8] Two other end-members are referred to as protohematite and hydrohematite.

Iron from mine tailings

Hematite is present in the waste tailings of iron mines. A recently developed process, magnetation, uses huge magnets to glean waste hematite from old mine tailings inMinnesota's vast Mesabi Range iron district.[9]

Discovery on Mars

The spectral signature of hematite was seen on the planet Mars by the infrared spectrometer on the NASA Mars Global Surveyor ("MGS") and 2001 Mars Odysseyspacecraft in orbit around Mars.[10] The mineral was seen in abundance at two sites[11] on the planet, the Terra Meridiani site, near the Martian equator at 0° longitude, and the second site Aram Chaos near the Valles Marineris.[12] Several other sites also showed hematite, e.g., Aureum Chaos.[13] Because terrestrial hematite is typically a mineral formed in aqueous environments, or by aqueous alteration, this detection was scientifically interesting enough that the second of the two Mars Exploration Rovers was targeted to a site in the Terra Meridiani region designated Meridiani Planum. In-situ investigations by the Opportunity rover showed a significant amount of hematite, much of it in the form of smallspherules that were informally named "blueberries" by the science team. Analysis indicates that these spherules are apparently concretions formed from a water solution.