Many people think of garnet as a gemstone, but did you know that only a portion of garnet is qualified for use as such? Most garnet is mined for industrial applications because of its abrasive nature. It is commonly used in sandpaper, sandblasting and water filtration.
Garnet is not just one mineral, though; the term garnet is used to describe a group of silicate minerals with a hardness of around seven on the Mohs scale. The six most common of these include:
- Almandine, which is red or brown in color
- Pyrope, which is red to purple in color
- Spessartite, which is orange to red to brown in color
- Andradite, which is green, yellow or black in color
- Grossular, which is green, yellow, red, pink or clear in color
- Uvarovite, which is green in color
Other types of garnet include:
Each of these garnet types has a different chemical composition, which determines its color. For example, garnets composed of calcium are greenish in color, while the garnets composed of aluminum, iron or manganese are reddish in color.
Here are some other facts about garnet that may surprise you.
1. Some varieties are color changing
Certain varieties of garnet change color when viewed under different light. The garnet will appear one color when viewed under natural light but will appear another color when viewed under incandescent light.
2. Until the late 20th century, garnet was thought to exist in every color but blue
When most people think of garnet, a red gemstone immediately comes to mind. The name is derived from “gernet,” a 14th century word meaning a deep red color. It also comes from the Latin “granatus,” which means grain seed.
While red is the most common, garnet can be found in many colors. It can be colorless, white, gray, brown or black. It can also be yellow, green, pink, purplish red, orange-red and violet red.
Until the late 20th century, garnet was said to exist in every color but blue. However, a discovery in Madagascar in the 1990s revealed garnets that changed from greenish blue to blue-green in daylight to purple in incandescent light.
3. It is the birthstone for January
Garnet has been the birthstone for those born in January since 1912. It is also Connecticut’s state mineral, the gemstone of New York and represents a second anniversary.
4. It was a popular gemstone in ancient times
Jewelry inlaid with garnets was buried with many Egyptians so they could have it in the afterlife. The gemstone was used for trading purposes in Rome, and in signet rings to create wax seals for securing important documents.
More about garnet
Located all around the world in metamorphic, igneous and sedimentary rock, most garnet forms in areas of high heat or pressure, which alter the composition of the mineral’s structure to one that can sustain the environment. Garnets begin as tiny grains that grow over time to include the surrounding rock; therefore, garnet is often found as an accessory mineral in certain types of igneous rock (think about the dark red crystals you may see in a granite countertop).
Methods of mining garnet from the earth vary. Open pit mining is common for hard rock locations, as is hand mining, depending on the mine’s location. Garnet extracted from alluvial deposits is done so using backhoes and draglines.
After the ore is mined, liberation of the garnet fraction begins with size reduction through use of machines like Jaw Crushers, Impact Crushers, Cone Crushers, rod and ball mills, depending on the deposit or the market. Liberated garnet is often separated from the gangue minerals through gravity concentration methods, such as Hydrosizers™ or spirals, or by froth flotation. The concentrate is then dried and sorted. The particles are screened into various market sizes and packaged for distribution.