With their deep red color and enduring hardness, garnets have been valued for both their beauty and their practical nature for centuries. Legend holds that Noah used a garnet lantern in the bow of the ark to guide him through the night. Deep red garnets were prized in Victorian jewelry and were believed to protect their wearer from nightmares. Found in Africa, Brazil, India, Madagascar, Canada and the United States, garnets have many decorative and industrial uses.
What Are Garnets?
Garnet actually refers to a group of minerals that are similar in their composition and properties. Composed of silica and one of several metal molecules, garnets don't cleave like diamonds and other faceted jewels. Instead, when broken they fracture sharply. Garnets are very hard, from 6 to 7.5 on the Mohs hardness scale, compared to 10 for diamonds and 3 for calcite. This hardness, and the sharpness of crushed garnet, makes it ideal for many industrial purposes.
The name garnet comes from the Latin word "granatium," which means pomegranate. Deep red garnets were thought to resemble pomegranate seeds. At some point, the "r" and "a" in granat were transposed, and the stones became known as garnets.
The size and quality of garnet determine how it is used. Only the largest, most perfect specimens go into jewelry.
Almandine or almandite ranges in color from black to dark red to orange to brown. The color comes from magnesium and iron in the molecules.
Andradite and grossular garnets include the highly prized green garnets. Andradite draws its yellow, green and brown coloration from calcium and iron. Andradites are rare and valuable, prized for their luster and a favorite with jewelers. Grossular or grossularite can be green, red, yellow or orange and may even be clear. Like andradite, it also contains calcium and iron. Some grossular garnets are a deep green, resembling jade and are known as African jade. They are sometimes carved into animals, flowers or decorative figures. While both andradite and glossular contain calcium and iron, glossular is harder, but andradite is more brilliant.
Another green garnet is Uvarovite, a chromium-bearing garnet that is always green. Its bright, emerald color makes it a sought-after drusy gem for jewelry. Drusy gems consist of tiny crystals deposited on a surface, rather than a single, large cut gem.
Pyrope garnets are always red, ranging from deep red, almost black, to purplish red, due to the presence of chrome. The name rhodolite comes from the Greek word for rose, "rhodo," which refers to the stone's lovely pink-to-red color. Rhodolites are among the most expensive and prized garnets for jewelry.
Spessartine is bright yellowish orange to orange-red, due to the presence of manganese and aluminum. It is also known as spessartite, but this is also the name of a different kind of rock.
Sanding and Polishing
The majority of garnets today are used as industrial abrasives. Garnet is crushed, then graded by size. Garnets are made into sandpaper, sanding belts, discs and strips. Garnet particles are used to polish wood and glass, especially optical glass.
Garnets are also used in abrasive powders and as the abrasive mixed with water and blasted through a jet. Unlike sand or silica, which were previously used in water and sand blasting, garnet doesn't break down during these processes, so can be recycled to be used over and over.
Other Industrial Uses
Garnet particles are mixed with water and fired in a high-speed jet in a process known as water jet cutting. Water jet cutting slices through metal and even granite with precision and with less dust and noise than other cutting methods.
Because garnet is inert and resists chemical degradation, it's used in water filtration. Garnet also sees use in the manufacturing of computer chips.
Garnet is the birthstone for January. Considered a semiprecious stone, garnets occur in every color but blue, but are most associated with a deep red color. Garnets vary in degree of transparency. Garnets can be hard to distinguish from rubies with the naked eye, as they share similar properties.
- Photo by Jarno http://www.flickr.com/photos/jaja_1985/167345135/