Double Refraction: -0.28
Named after the Greek word for "blood" or "of the blood", hematite is a heavy mineral with a bright metallic lustre. Crystals of hematite, which are rare compared to the other forms of the stone, usually occur in thin plates, sometimes as splinters, and other times curled up, resembling a metal rose. Hematite is often very dark in color, almost pure black, but will leave a red streak. This is because the crystals are really red, and the large cluster becomes too opaque to let the red color out. The coloration of some gems, such as sphene, comes from hematite. Scientists also think areas of Mars that have grey1 hematite used to contain water in some quantity, as the stone can be formed through sedimentary depositing.
Ancient cultures often believed that hematite was formed from battles. They thought the blood spilt seeped into the earth and crystalized to make hematite. Hematite is actually formed in two main ways. Hematite is often found in several igneous rocks, especially cooled lava. It's formed under the proper oxidizing conditions. Another way is through sediment deposits that dry out underneath the hot sun. Sandstone is red due to the presence of hematite. Geographically, hematite is found in Cumberland in England, the Island of Elba, Saalfield in Germany, Norway, Sweden, Spain, Brazil, New Zealand and the Great Lakes region of the United States.
Several different forms of hematite occur in nature. Here are a few more common types:
- Hematite Rose: A circular arrangment of thin, plate-like crystals which swirl together similarly to rose petals.
- Tiger Iron: 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.
- Kidney Ore: A massive botryoidal form that looks like lumpy kidney-esque masses.
- Oolitic Hematite: A sedimentary formation with a reddish brown color, an earthy lustre and is composed of small rounded grains.
- Specularite: A micaceous or flaky stone that is sparkling silver gray. The name comes from the latin word for mirror, as the Romans often forged the stone into them.
Galen, an ancient egyptian medical teacher noted that hematite has very good astringent properties. He wrote that tumors on the eyelids could be cured with hematite that was dissolved in egg whites. If the eye was just inflamed, he suggest a similar solution, but with water replacing the eggwhites. Drops of the solution were to be dropped into the eye through a glass tube. The solution was to be made thicker and thicker, by adding more powdered hematite, until it had to be dipped on to the point of the tube to apply it.
However, thanks to modern medicine hematite is no longer used in such a manner. Instead it is principly an ore and counts for about 90 percent of commercial iron produced in the United States. Huge quantities are mined yearly for industrial production. In the recent past, it was ground up and used for red and brown pigments. However, red and brown pigments can now be made for less expense without using hematite. Polished hematite can sometimes be found as rings, beads or cut into cabochons for brooches and pendants. One of the earliest uses for hematite jewelry was for signet rings.
1: This is important for the Life on Mars debate. The red hematite is small grains, whereas the grey hematite is bigger crystals, signifying volcanic activity or a body of water. While a volcano would not mean too much for life on Mars, afaik, liquid water would, as all life needs water.
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The Magic of Jewels and Charms, Dr. George Frederick Kunz. J.B. Lippincott company, Philadelphia and London, 1915