Where to find iolite gemstones in nature

Group of faceted iolites set in a golden cross.
Iolites are some of the more attractive
gemstones, but few jewelers keep them on
hand because of relatively low-value and
rarity.

Finding iolite gemstones is not easy as there are not many guides. But if your region of exploration has the right metamorphic conditions, such as in the central Laramie Mountains and possibly the Copper Mountain in the Owl Creek Mountains, you might consider searching for the gemstone. The conditions for metamorphic iolite deposits are favorable in regions where aluminum-rich schists and gneisses are found and where the metamorphic triple point was reached to produce regional kyanite schists, andalusite schists and sillimanite schists. 

Cordierite mica schist, Palmer Canyon. Three faceted iolites
 sit on the edge of a large iolite porphyroblast. 

First check to see if there are metapelites (also referred to as pelitic schists). These schists are aluminum-rich schists with aluminum-rich minerals such as mica, garnet, staurolite, andalusite, kyanite, sillimanite, cordierite and/or corundum. Mica schists are typically strongly foliated and may contain some large porphyroblasts within the matrix. If you find any mention of cordierite in a geological description in an area, you may have chance of finding gem iolite in those rocks, as most geologists have little to no background in gemstones and iolite is often overlooked.

Cordierite (iolite) has a low-specific gravity (2.57 to 2.66) similar to quartz, so panning streams for this gem will not be effective. The gem has a good hardness of 7 to 7.5 on Moh's scale, making it slightly harder than window glass. Its crystal habit is typically massive to granular and may occur as pseudo-hexagonal crystals, and rarely as prismatic twins. Twinning planes are common in the crystals, and cleavage is typically fair to poor. It breaks in a conchoidal fracture (like glass) and has greasy to vitreous luster. Specimens are strongly pleochroic that is visible in thin, transparent grains when viewed at different angles in sunlight, or viewed with polarized light.

To find this gemstone, search  favorable metamorphic terrains. Good places to start searching are geological reports that describe the presence of mica schist containing blue cordierite. Geologists, who are not taught to recognized gemstones, often describe the mineral but seldom mention transparency or gem-character. SO it is likely there are cordierite deposits described in various university geological theses and survey reports, that may have gem-quality iolite. Even the Laramie Mountains in Wyoming, which has an abundance of metapelites near the central to northern part of the range west of Wheatland

Large porphyroblast of iolite with distinct parting planes and pseudo-hexagonal crystal habit,
Palmer Canyon, Laramie Mountains, Wyoming (photo by author).

Another important characteristic is to search the literature for descriptions of kyanite, sillimanite and/or andalusite. These minerals form under similar conditions as metamorphic iolite gemstones.

Group of faceted iolites and rubies from Palmer Canyon, Wyoming

Beautiful, large iolite porphyroblast in mica gneiss from
Palmer Canyon, Wyoming.

Reaction rim at edge of large, 1,720-carat iolite gemstone, Palmer Canyon, Wyoming (photo by
author).

Outcrop of iolite gem cut by milky quartz vein, Grizzly Creek
Wyoming. Photo by author.