Iolite Quality Factors
Iolite possesses two distinctive features—a beautiful, violetish blue through slightly violetish blue hue derived from iron and a striking, eye-visible pleochroism. Its pleochroic colors differ with its bodycolor. Iolites that appear violet display light violet, dark violet, and yellow-brown pleochroic colors. Bluish iolites display colorless to yellow, blue-gray, and dark violet pleochroic colors. From some angles, then, a bluish iolite can actually appear completely colorless or yellow, and a violetish iolite can look brown. Some gems can look grayish or nearly colorless.
Iolite is commonly transparent, with relatively few inclusions. It can be found in all shapes and has even been carved to beautiful effect.
Iolite can contain inclusions that cause various phenomena. Occasionally, iolites with long, parallel, tubular inclusions are found. When the cut is oriented properly, these stones yield cat’s-eye gems.
Iolite containing numerous metallic, plate-like inclusions can be cut to display a sparkly effect known as aventurescence. When the platelets are brownish or reddish in color, the gem might be marketed as “bloodshot” iolite.
Because it is commonly transparent with relatively few inclusions, iolite is most often faceted. However, iolites can be cut into cabochons or carvings as well. They are frequently seen as beads, especially when the material is of somewhat lower quality.
The size range for a fashioned iolite is anywhere from 1 to 10 carats, but fine iolites over five carats are rare.