Hematite

What is hematite? Hematite is a mineral that can appear red, reddish-brown, steel gray or black. Its chemical composition is Fe₂0₃ (70% Fe, 30% O). The reddish colour is due to the presence of iron. Hematite is a common mineral and can be found in all types of rock--igneous, sedimentary and metamorphic. The University of Virginia web site defines a mineral as being a naturally occurring, homogeneous inorganic solid substance having a definite chemical composition. Minerals have the following properties: colour, streak, luster, striations, tenacity, and magnetism. Hematite that has a metallic luster is called specular hematite, or specular iron. Hematite can always be identified by its red streak regardless of the colour of the specimen.

Hematite can occur in some amazing formations. Concretions are compact mass of mineral matter, usually spherical or disk-shaped, embedded in a host rock of a different composition. Sandstone cemented with hematite can result in some interesting or unique rock formations. A geode is a sphere shaped rock, which contains a hollow cavity lined with crystals. It can be filled with the mineral hematite (or black hematite).

Why has hematite been in the news? Gray hematite was detected on Mars by the infrared spectrometer on NASA's Mars Global Surveyor (MGS) spacecraft in 1998. On Earth, gray hematite is found around hot springs or standing pools of water--places of water activity. Can the presence of gray hematite on Mars mean that Mars once had water or has hidden waters? Scientists are determined to find out. The landing site for the Mars Rover Opportunity was chosen to be a place called Meridiani Planum, a plain near the equator. Why? This site contains an ancient layer of hematite. How did it get there? Was it water activity or volcanic activity? NASA hopes Opportunity will tell the tale.

And the news from Mars has been exciting. Opportunity examined an outcrop of rock that had little spherical grains embedded in it like blueberries in a muffin. It has been determined that the major mineral in these blueberries is hematite, leading scientists to deduced that the Martian spherules are concretions that grew inside water-soaked deposits. Scientists now believe that Opportunity is on the edge of a Martian salty sea.

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