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Garnet
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General Information:
The name garnet is derived from the Latin word
granatus "grain," referencing the pomegranate fruit which has
red seeds similar in color, shape, and size to the garnet. The most common
color of garnet is red but there are many other colors including, orange,
yellow, green, pink, purple, brown, black, and colorless. Garnet is the
traditional birthstone for January, and has been used for many thousands of
years. References towards the stone can be found in both the Bible and the
Koran. Garnet was also used in North, South, and Central America by Indian
tribes who thought of it as sacred. Garnet is a semiprecious gemstone that is
popular in jewelry, and is used as an abrasive (used for smoothing and
grinding) because of its ability to be recycled, cost efficient, and it is easy
to clean.
While there are many types of garnet, they have essentially the same isometric
crystal structure varying in their physical properties and chemical
composition. There are six common species of garnet based on their chemical
composition which are; pyrope, almandine, spessartine, grossular, uvarovite,
and andradite. From these six, two main groups are formed: pyralspite (pyrope,
almandine, spessartine), and ugrandite (uvarovite, grossular, andradite). A
natural garnet's composition generally falls somewhere between the two main
groups and are rarely if ever found precisely matching the pure species. A
variety of garnet called mozambique is red to orange-red in color. Its
chemical composition is a mixture between pyrope and almandine, averaging a 1:1
mixture respectively. Another variety using both pyrope and almandine is
rhodolite, a rose-red to purple garnet with a composition mixture
average of 2:1 respectively.
Grossular garnets that are brown, orange-red, or yellow-orange are known as
hessonite. Rare forms of garnet such as tsavorite and
demantoid occur when ions such as Cr3+, V3+ and Ti3+/4+ replace the common
composition of the mineral. Color change garnet can also be found. This color
change occurs when the stone is placed under fluorescent light versus
incandescent light. The cause of the color change is impurities, in large
amounts, of vanadium or chromium in malaia garnets.
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Origin:
Garnet deposits have been discovered in Africa, Argentina,
Australia, Brazil, Canada, Finland, India, Madagascar, Myanmar (Burma), Russia,
Scotland, Sri Lanka (Ceylon), Switzerland, Tanzania, and the United States (In
the states of; Arizona, Colorado, Georgia, Idaho, New Hampshire, New Mexico,
North Carolina, Pennsylvania, Utah, Virginia). |
Common Treatments and Lab Created
Forms:
The only current garnet treatment known and used is on
demantoid garnet. It is sometimes mildly heated to enhance the color. Natural
forms of garnet are not currently made in laboratories, but there are simulants
and cubic zirconias with similar color to garnet. |
Physical Properties:
Moh's Scale Hardness: 6.5-7.5
Specific Gravity: 3.4-4.3
Refractive Index: 1.72-1.94
Fracture: conchoidal, somewhat brittle
Crystal Habit: rhombic dodecahedra or cubic
Colors: Virtually all colors
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