Description
Hematite (from Greek: αιμία, haima, blood) is a mineral composed primarily of ferric oxide crystals (iron(III) oxide, Fe2O3), one of the iron oxides. It occurs alongside other varieties such as red bloodstone and grayish-black to black iron luster and micaceous iron. The mineral has a hardness of between 5 and 6. The so-called streak, or streak color, the color the mineral imparts when rubbed over an unglazed porcelain dish, is usually a characteristic blood red—from which the mineral derives its name. The mineral may contain traces of magnesium, manganese, and titanium. Hematite occurs both as a gangue mineral and in sedimentary layers. It is often the cause of the red coloration of many rocks. Other iron ores such as magnetite, limonite, and iron spar often occur alongside hematite. When magnetite has been converted to hematite, it is called martite. The mineral is found worldwide: in Europe, in Germany, among other places, in the Lahn region, where the world's largest concentration of iron ore is located, in the Eifel, the Harz mountains, and the Thuringian Forest. It is also found in England in Cumberland and North Lancashire, in Belgium in Vezin and Namur, on the Italian island of Elba, and in Spain. In Africa, Algeria is a notable producer, and in the United States, it is found near Upper Lake and the Missouri River. More than half of the world's production currently comes from China, Brazil, and Australia. The mineral also occurs in high concentrations on the surface of Mars, giving the "Red Planet" its characteristic orange-red color. In its pure state, hematite consists of 70% iron, making it the most important iron ore. Iron is extracted by reacting it with carbon at high temperatures. Hematite is also used as a polishing agent and, due to its high reflectivity, has long been used as a mirror. The red color and the fact that hematite is non-toxic make the mineral very suitable as a pigment. It was already used in the Stone Age for rock carvings and body painting. Artists use pressed hematite pencils for drawings and sketches. Such pencils are soft and color well. Red bolus, a highly clay-containing hematite, is often used as a base coat for gilding. As a pigment, hematite is suitable for painting ceramics and dyeing threads for carpets.
Tiger's eye is a variety of quartz. The stone's color is yellow-brown to brown, streaky, and opaque. Its locations include Africa, India, Mexico, California, and Australia. Tiger's eye is formed by the silicification of black-blue asbestos fibers called crocidolite. This process creates solid inclusions of hair-like crystals within the quartz. The oxidation of the original crocidolite fibers creates the stone's golden, lustrous limonite fibers. Tiger's eye is so named because the stone reflects light reminiscent of a tiger's eye. This slit-shaped light effect is called chatoyancy or "cat's eye." When the stone is cut cabochon (sphere), the beautiful cat's eye effect is most visible. The stone's color gives it its name: the red variety is called Cat's Eye, the blue Falcon's Eye, and the yellow Tiger's Eye (golden yellow, golden brown).
