IN THE PRESS
A Brief History Of Garnets, The January Birthstone
January 06, 2017 | By Kristin McCabe
Garnets are a set of closely related minerals that form a group, resulting in gemstones in almost every color. Red garnets have a long history, but modern gem buyers can pick from a rich palette of garnet colors: greens, oranges, pinkish oranges, deeply saturated purplish reds, and even some blues.
Red garnet is one of the most common and widespread of gems, found in metamorphic rocks (which are rocks altered by heat and pressure) on every continent. But not all garnets are as abundant as the red ones. A green garnet, tsavorite, also occurs in metamorphic rocks, but it’s rarer because it needs unusual rock chemistries and special conditions to form.
Demantoid is a rare and famous green garnet, spessartine (also called spessarite) is an orange garnet, and rhodolite is a beautiful purple-red garnet. Garnets can even exhibit the color-change phenomenon similar to the rare gemstone alexandrite.
All garnets have essentially the same crystal structure, but they vary in chemical composition. There are more than twenty garnet categories, called species, but only five are commercially important as gems. Those five are pyrope, almandine (also called almandite), spessartine, grossular (grossularite), and andradite. A sixth, uvarovite, is a green garnet that usually occurs as crystals too small to cut. It’s sometimes set as clusters in jewelry. Many garnets are chemical mixtures of two or more garnet species.
Pyrope and almandine range in color from purple to orangy red. Spessartine is found in a variety of orange colors, while andradite comes in yellow and yellowish green. Grossular has perhaps the widest color range of any garnet species, from colorless through yellow to reddish orange and orangy red, to a strong, vibrant green.
Gemologists and colored stone dealers further subdivide some garnet species into varieties depending on color. For example, demantoid is a brilliant green variety of andradite that’s highly prized by collectors. Both tsavorite and hessonite are varieties of grossular. Tsavorites are green, while hessonite ranges from orange and orangy red to brownish red. Rhodolite is a purplish red variety.
Many garnets are cut into standard shapes and standard sizes to allow easy setting into jewelry. This is especially true of many red garnets. Expensive garnets like fine-quality tsavorite are cut into shapes and cutting styles that allow more of the weight to be retained from the rough.
Demantoid is often cut to exact proportions that allow the best possible display of its fire. Garnets are also popular for designer cuts and carvings. Red garnets are classic materials for cutting into cabochons and beads. They are commonly found to have high clarity and to be very transparent.
All above information and pictures come from: GIA (Gemological Institute Of America) www.GIA.edu
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