Garnets are a group of related silicate minerals that vary slightly in their chemical composition but have similar crystal forms and physical properties. These minor differences give rise to a large array of colors and a Mohs Scale of Hardness of 6.5 to 7.5 making them desirable as gems. Because of their hardness, garnets have industrial uses and are often used as abrasives.
Formation
Garnet typically originates in metamorphic rocks where pre-existing minerals undergo recrystallization in response to intense heat and pressure. The transformation process triggers the growth of garnet crystals in various host rocks, resulting in its captivating diversity of colors.
Types of Garnets
Garnets are one of the most complex gem mineral groups in the world. There are five main varieties.
Almandine: Recognized for its deep red to brownish-red hues, almandine garnet is rich in iron and aluminum. It’s often found in metamorphic rocks such as schistst and gneiss.
Pyrope: Characterized by its intense, fiery red color, pyrope garnet derives its name from the Greek “pyropos,” meaning “fire-eyed.”
Spessartine: Known for its vibrant orange to reddish-brown shades, spessartine garnet forms in granite and pegmatite environments. Manganese gives it a unique coloration.
Grossular: Grossular garnet comes in a range of colors, including green, yellow, brown and even colorless. It’s found in metamorphic rocks and prized for exceptional clarity.
Andradite: Andradite garnet encompasses several subvarieties, with colors spanning from green (demantoid) to black (melanite). These garnets are often associated with skarn deposits. Demantoid is considered to be the most valuable of all the garnets.
Celebrated Garnet
Garnet is the birthstone for January and is the state gemstone for Connecticut, New York and Vermont. In the metaphysical realm, garnet is thought to affect the heart both physically and emotionally. It is also thought that garnets improve health in general.
Where to Find
Notable places to find garnets in the United States include Alaska, where beaches along the Kenai Peninsula are known for yielding almandine and pyrope varieties as they are carried downstream by rivers; the Barton Mine in New York where rockhounds can dig for garnets, especially almandine and grossular; and the desert southwest, particularly Arizona, where garnet crystals weather out of rocks and can be found near ant hills.
This story about garnets previously appeared in Rock & Gem magazine. Click here to subscribe. Story by Richard Gross and Pam Freeman.
