Education, Garnet

GARNET

MINERAL: Garnet group
CHEMISTRY:
Almandine- Fe3Al2(SiO4)3
Andradite- Ca3Fe2(SiO4)3
Grossular- Ca3Al2(SiO4)3
Pyrope- Mg3Al2(SiO4)3
Rhodolite- (Mg, Fe)3Al2(SiO4)3
Spessartine- Mn3Al2(SiO4)3
COLOR: All colors
REFRACTIVE INDEX: 1.714-1.888
BIREFRINGENCE: None
SPECIFIC GRAVITY: 3.47-4.15
MOHS HARDNESS: 6.5-7.5

Sources

Russia, Myanmar, India, Pakistan, Afghanistan, Iran, Sri Lanka, Kenya, Tanzania, Namibia, Brazil.

Birthstones & Anniversaries

Garnet is the birthstone for January and the gem for the second anniversary.

Description

Garnets are a set of closely related minerals forming a group, with 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. But not all garnets are as abundant as the red ones. A green garnet, tsavorite, is rarer and needs rarer rock chemistries and conditions to form.
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.

ACCESSORIES

History

Thousands of years ago, red garnet necklaces adorned the necks of Egypt’s pharaohs, and were entombed with their mummified corpses as prized possessions for the afterlife. In ancient Rome, signet rings with carved garnets were used to stamp the wax that secured important documents.
The term carbuncle was often used in ancient times to refer to red garnets, although it was used for almost any red stone. Carbuncle was thought to be one of the four precious stones given to King Solomon by God.
Centuries later, in Roman scholar Pliny’s time (23 to 79 AD), red garnets were among the most widely traded gems. In the Middle Ages (about 475 to 1450 AD), red garnet was favored by clergy and nobility.
Red garnet’s availability increased with the discovery of the famous Bohemian garnet deposits in central Europe around 1500. This source became the nucleus of a regional jewelry industry that reached its peak in the late 1800s.

GARNET QUALITY FACTORS

Garnets are a group that includes a number of different minerals, so appearance can vary widely. The first thing a buyer of garnets needs to be aware of is the wide variety of garnet types.
At first, the sheer number of garnet varieties can seem bewildering. It helps to think of the different types of garnets in terms of color.

Color

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.

Clarity

Typical garnet clarity depends on garnet type. For example, the red garnets almandine, pyrope, and rhodolite typically do not have eyevisible inclusions. Some of the orange garnets, like spessartine and hessonite, often have eye-visible inclusions.
Grossular is typically translucent, making it popular for cabochons, beads, and carvings.

Cut

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.

Size and Weight

Garnets can be found in all sizes and weights. Some garnets, like demantoid and tsavorite, are more commonly found in small sizes, so their value goes up significantly with size. Other garnets, like almandine, are far more common in larger sizes so there’s no dramatic rise in value as size increases.

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