6-ray Idaho Star Garnets (Asteriated Almandine) from Emerald Creek are the most valuable and best quality star garnets known. Most star garnets from this locality are a very dark purple with or without zoning. They show their color best in sunlight or other bright, direct lighting. Very few are dark red and show red in the sun, but the star is generally weak. It is extremely rare, but also possible, to find a very nice 6-ray star on a star garnet that shows red or pink in the sunlight. The unique color of Emerald Creek garnets comes from mineral impurities within the garnet. The core of the Emerald Creek garnet is rich in manganese whereas the rims are rich in iron and magnesium. Some calcium zoning is present as well, with more calcium towards the rim of the crystal. Some star garnets have inclusions that reflect the light in such a way that looks as if the garnet has fine glitter just below the surface. I have heard this referred to as "fire", but is not the same thing as one would consider "fire" in other gemstones. Red star garnet cabochons with high translucency will have a traveling red spot as you rotate them around in direct sunlight. This is referred to as a "pigeon eye".
The Star phenomenon comes from a sufficient amount of rutile, a mineral composed of titanium oxide, arranged along the crystal planes of the stone. The rutile in the star garnet is commonly refered to as "silk". Not all garnets from the Emerald Creek site will star. Four-ray star garnets greatly outnumber six-ray star garnets. It is very common for a six-ray star garnet to have two dim rays. The number of rays are based on the concentration and orientation of the tiny rutile needles. Since the rutile is more concentrated toward the center of the crystal, and the crystal structure is isometric forming dodecahedrons (12 sided crystals) or some modification thereof, the asterism (star) is much more difficult to orient than a star sapphire or ruby. There are very few cabochon gem cutters that are able to correctly orient a star garnet, and even fewer that are able to maximize the size and quality attainable from the rough material.
A clean, high quality star garnet larger than 10
carats will most likely demand a premium. It is common for larger star
garnets to have flaws. Since most natural fractures penetrate to the
center of the crystal, it is often impossible to eliminate a fracture and
still correctly orient the star. It is also rare to find a very small
(under 6mm) well cut star garnet.
In an attempt to standardize star garnet quality grading, Dale Bramlette has developed a chart which you may find useful: http://www.idahogems.com/sgrades.htm .
High quality star garnet and any star garnet displaying 6-rays is extremely rare and undervalued due to its obscurity. While star garnets can be found in a variety of places, Idaho Star Garnets are the best known and of the best quality. I have heard of star garnets (mostly 4-ray) from several other locations including: India (red), Russia (brownish purple), Africa (purple), Brazil (purple), and North Carolina (purplish brown, usually quite fractured internally). If you're ever in doubt of their rarity and uniqueness, just ask for a gem dealer to find a match to a high quality Idaho star garnet that you obtain. I generally cut two gems from the same crystal in order to make a matched set for earrings.
Please note: This site is mainly for informational purposes. Due to other time commitments, I may not be able to offer cutting or jewelry services. Please contact me for more information.
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