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Star Garnet

By Mason

November 11, 2014

Idaho Six ray star garnet

Introduction

The star garnet is very rare, only found in India and Idaho in the United States. Although it was declared the state gemstone of Idaho in 1967, many people do not know about it. In Idaho the star garnets are found in Emerald Creek, next to India it is the only other producer of star garnets known at this time. And the great thing is that anyone can find star garnets at the Emerald Creek mining area. So if your ever in northern Idaho you might want to go to the mining area yourself, where you'll have a chance to find your own treasures!

History

According to Stewarts Gem Shop, Gene Stewart's father, Dudley Stewart discovered the method of cutting the Idaho garnet, from the emerald creek area in order to reveal the star in the stone. He pioneered the Idaho star garnet and brought it to the markets in 1951. In the same year, he brought his finished garnets to the Sacramento CA. Gem and Mineral show where they where a big hit. They also say that the Idaho star garnets are the best you can get from anywhere else in the world.

Emerald Creek Mining Area

It is available to the public from Memorial Day through Labor Day, and for a small fee you can buy a permit to dig from a stock pile of garnet bearing gravels on the site and try to find some star garnets. All the tools you need to find the garnets are provided by the site to anyone with a permit. And the great thing is there is enough garnets that you're nearly guaranteed to find some, if you know what your looking for and are willing to work for it. Our family visited the Emerald Creek mining area two times, for about 3-4 hours each, and with all six of us working, we ended up with around 40 ounces total!

 

Stockpile at Emerald Creek Mining area

Stockpile at Emerald Creek. All your gravel (with garnets) is collected here.

 


Sifting area at Emerald Creek

Sifting site at Emerald Creek, here you take the dirt and gravel from the stockpile and sift out the dirt and small sand.

 

Sluice area at Emerald Creek

Sluice site at Emerald Creek, where you clean the sifted gravel and find your garnets.

 

Identification

Rough star garnets collected at emerald creek

It is important to know what your looking for, garnets from this area are black, to plum color in the rough. You will be looking for garnets in the sluice after you wash all of your gravel to clean and wet it. Then the garnets will look dark purple, unlike most of the other stones. This way it will be much easier to identify your garnets and separate them from anything else. And remember, if it looks suspicious just keep it, you can always throw it away later.

Cutting of garnets

Some of our Star Garnets after being cut

Some of our final cut garnets.


Once you have your garnets you'll need to have them cut to show a star. To display a star the garnet must be cut in a specific way, that is en cabochon. The cabochon cut is a smooth cut stone with a flat bottom and domed top. Before that, the garnets must be tested by grinding them smooth and to a polish where the gem cutter sees the silk. Then the star can be oriented and the garnet can be ground to it's final shape and given a high polish. The test also tells the gem cutter the quality of the final star, so they may decide to finish them or not.

Some of our Star Garnets in the testing stage

The same garnets as above in their testing stage.


The cut of star garnets is important to have a stone with the best possible star. The better the cut the more centered and brighter the star can be. This does not mean every stone will have a good star, it just means the cut quality makes a big difference. We took our garnets to Stewarts Gem Shop to have them cut (they are shown above).

Asterism

So what causes the star? The star effect displayed in Star garnets, as well as other stones like corundum and quartz is called 'Asterism'. Asterism came from the Greek word 'aster' which is star. Asterism is an optical phenomena caused by small fiber like inclusions of rutile (titanium oxide, also called 'silk' by gem cutters) running along the faces of some gemstones. When light reflects off this rutile it can be seen as a star with four or six rays (in corundum, a star may have twelve rays). Because of the crystal structure of garnet (Rhombic Dodecahedron) it most commonly has four rays, but can occasionally display a six ray star. For this reason the six rayed garnets are more rare and considered superior.

As you can see from the diagram there are several four-ray intersections in a rhombic dodecahedron.

Rhombic Dodecahedron, the shape of a garnet crystal

Mineral Properties and crystal structure of garnet

There are several different types of garnet, because of this they can come in many different colors, like purple, green, brown, blue or even colorless. The Idaho star garnet is of the almandine (aluminum containing) type. So it's color is dark purple or plum to red or pink, when light is shining through it. This type of garnet is the hardest variety of garnet at 7.5 on the mohs hardness scale. Garnet is a crystal that grows in metamorphic rock. It is harder than the rock it grows in, so its bedrock is eroded away and rolled down the creek, progressively being broken away by the creek until only the garnet is left. The garnets are then damaged by the creek once they're no longer protected by their containing stone. So depending on how long ago their containing stone eroded away, the garnets may be damaged. Because of this it is fairly rare to find a full crystal, it's exterior will probably be damaged but if it has not been cracked and broken, then it is a full crystal. Below are some examples of full crystals.

Some examples of full garnet crystals

Research Links

Garnet

Garnet - Wikipedia

Garnets - International Colored Gemstone

Star Garnet History

Idaho 281 Star Garnet - Stewarts Gem Shop

Star Garnet Idaho State Gemstone

Asterism

Star Stones (Asterism)

Study of Gemstone Phenomena: Asterism

Asterism in Gems - JewelInfo4U

Cutting of Star Garnets

Cabachon Cutting Style

Star Garnet Orientation - Stewarts Gem Shop

Before our apps

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