Iolite - An Extraordinary Gem
Iolite is the gemologists term for the mineral cordierite. It is a magnesium-iron-aluminum silicate with iron present in solid solution with magnesium, such that there exists both magnesium-rich cordierite and iron-rich cordierite (refereed to as sekaninaite). Thus the chemical formula for the end members of the solid solution series is (Mg,Fe)2Al3(Si5AlO18) and (Fe,Mg)2Al3(Si5AlO18). The mineral was named after a French geologist by the name of Louis Cordier in 1813.
Good quality cordierite is often used for gemstones. The name "iolite" comes from the Greek word for violet. This stone is also referred to as dichroite, a Greek word meaning "two-colored rock", a reference to cordierite's strong pleochroism. It has also been called "water-sapphire" and "Vikings' Compass" because of its usefulness in determining the direction of the sun on overcast days, the Vikings having used it for this purpose. When prospecting, iolite is difficult to find with a gold pan unless you are panning near the source rock. The best way to prospect for iolite is to search for metamorphosed aluminum-rich rocks such as biolite schist and gneiss.
Gem quality iolite varies in color from sapphire blue to blue violet to yellowish gray to light blue as the light angle changes. It is softer than sapphire, is orthorhombic and often has a massive to pseudo hexagonal crystal habit. It is described in Australia (Northern Territory), Brazil, Burma, Canada (Yellowknife area of the Northwest Territories), Finland, Germany, Greenland, India, Madagascar, Myanmar, Mozambique, Namibia, Norway, Sri Lanka, Tanzania, United States (Connecticut and Wyoming) and Zimbabwe. The largest iolite crystal found on either weighed more than 24,000 carats, and was discovered in Wyoming.
Iolite was all but unknown in Wyoming before my 1996 discover of fabulous gem-quality iolite at Palmer Canyon to the west of Wheatland, Wyoming. The only other report of iolite in Wyoming at that time was by John Sinkankas in a gemstone book that alluded to a giant, rich, iolite deposit, but gave no specifics, no location, and left one wondering where could this deposit be located. Even to this day, we do not know what deposit or where Sinkankas was referring to. Could it have been the Grizzly Creek deposit or the Sherman Hills-Ragged Top Mountain deposit? Or was he describing a altogether different deposit in Wyoming or even in another state such as Montana? We will likely never know. Before his passing, I contacted Sinkankas to ask about the reference, but he could not remember anything about the occurrence or deposit.
After the Palmer Canyon deposit, I came across three other iolite deposits in the same region of of the central Laramie Mountains and predicted where other iolite deposits might be found in Wyoming. Two of the deposits I came across after Palmer Canyon are likely world-class multi-gem deposits containing iolite. The Grizzly Creek deposit is certainly of world class, but the Sherman Hills-Ragged Top remains uncertain, but likely is an incredible deposit. I had hoped to investigate this latter deposit, but I unfortunately ran into a roadblock and had to leave the deposit for someone else to investigate in the future, even though I had found some very high-quality gem iolite at the periphery of the deposit indicating that the deposit could have potential to host considerable gem material. Based on mapping, sampling and trenching before 1949, this deposit could host as much as 2.5 trillion carats in gemstones!!!
Giant iolite gemstones including the largest iolite gems in the world were discovered in the Laramie Mountains of Wyoming. Gemstones weighing >24,000 carats were recovered from Grizzly Creek with masses left in the outcrop that are estimated to include stones of more than a hundred thousand carts and some that could potentially top a million carats. Many of these were massive transparent stones and others were highly fractured but also transparent with excellent color.
The discovery of iolite gems at Palmer Canyon was followed by discoveries at Grizzly Creek, Sherman and Ragged Top Mountain, and Owen Creek. These latter deposits were and predicted to exist based on favorable geology (Hausel and Sutherland, 2000). And it is very likely other iolite and ruby deposits remain to be found in this region. These discoveries represent the largest iolite deposits and individual iolite gemstones found anywhere on earth. Yet, believe it or not, they remained undiscovered until 1996, 2004 and 2005. (Hausel, 2005b).
Gemologists refer to gem-quality cordierite as iolite that is also referred to as water sapphire. Geologists & mineralogists refer to this gem as cordierite. The mineral has also been labeled as dichroite.
Cordierite typically is found in the vicinity of other alumino-silicates in amphibolite-grade metamorphic terrains such as andalusite, kyanite & sillimanite. Host rocks include alumina-rich mica schists (metapelites). Cordierite is also found as a replacement mineral in alumina-rich syenite-anorthosite complexes & in some shales.
Iolite may form short prismatic crystals with rectangular cross sections as well as granular masses and nodules of various shades of blue, bluish-violet, gray and/or brown. Fresh cordierite has a hardness of 7 and specific gravity of 2.55 to 2.75. The hardness is favorable for durable gemstones. The principal deposits that supply much of the world’s market are Sri Lankan placers in spite of low specific gravity of the mineral (i.e., it is not favorably concentrated in placers).
Iolite exhibits strong pleochroism that varies from light gray, dark violet-blue, to light sapphire blue. The gem may appear deepest blue when viewed down the c-axis and light blue to light grey in other orientations. These color variations are one of the attractive features of this gem. Iolite is also often enclosed by a reaction rim of pinite or stained by limonite (Hausel, 2002).
Iolite is a beautiful stone that rivals tanzanite. However, tanzanite is much more valuable but only because of marketing strategies. Good iolite is every bit as attractive and wearable and should be valued similar to tanzanite, but it will take brilliant marketing strategies to promote the gemstone. The luster of iolite is vitreous and when polished, it becomes increasingly lustrous. Faceted iolite gemstones greater than 12-carats in weight are unheard of on the world market, even so, rough material collected at Palmer Canyon and Grizzly Creek included stones much larger than 12-carats. Some of the larger porphyroblasts weighed >100 carats with others of more than 1000 carats.
In Wyoming, cordierite has been found in gneiss with quartz and biotite as porphyroblasts with xenoblastic texture (Hausel, personal field notes, 1995). Worldwide, the highest quality gems are found as pebbles in Sri Lanka where much of the material sold on the internet is found and cut. With a marketing plan, Wyoming could easily control the world market of iolite and potentially promote this gemstone and bring a major new gem industry (mining, cutting, and marketing) to the Cowboy state. But it will take effort from the state legislature. Iolite currently sells for a trivial $15 to $30 a carat for the loose gemstones compared to tanzanite which sells for around $100 per carat. But loaded in jewelry, tanzanite can sell for more than $1000/carat. A good marketing ploy with a good story and a unique name, can bring much higher prices for iolite.
A few things Wyoming has going for it is its giant resources that could supply not only internet outlets, but also jewelry stores. Sri Lanka has a very unsteady supply of iolite gemstones resulting in few gems marketed in jewelry stores. Additionally, Wyoming has both magnesium- and iron-rich varieties that produce an array of blue gems from light blue to dark blue to amethyst blue to black.
Large nodular masses of iolite were discovered in two separate deposits in Archean (>2.5 billion year old) gneiss in Wyoming and a giant disseminated deposit may occur in the Laramie Range anorthosite-syenite batholith (Hausel 2002; 2004; 2006a). These deposits represent the largest in the world, but remain poorly explored (Hausel, 2005b).
Two deposits (Palmer Canyon and Grizzly Creek) are poly-gem occurrences with ruby & sapphire as accessory gems along with considerable kyanite (some gem-quality) in vermiculite and biotite schist and gneiss. Based on the metamorphic grade, there are also possibilities for other gems such as andalusite, sillimanite, and staurolite at these deposits. And not far from the Sherman Hills desposit, there is potential for spectrolite gemstones. And it doesn't end there. While conducting research at the Wyoming Geological Survey, we identified evidence for other ruby and sapphire deposits in this region as well as diamond deposits.
The metabolites in this area of the central Laramie Mountains represent enclaves of aluminous schist & gneiss. A third deposit in the vicinity of Ragged Top and Sherman Mountain is hosted by anorthositic-syenitic rocks (1.5 Ga).
Iolite was discovered in 1995 at Palmer Canyon during field reconnaissance (Hausel, 2002). The deposit lies along the eastern flank of the central Laramie Range 16 miles west of Wheatland within Archean quartzofeldspathic gneiss, granite gneiss, pelitic schist, and biotite-chlorite-vermiculite schist north of the Elmers Rock greenstone belt. To visit this area, fly to 'Palmer Canyon Rd, Wheatland WY 82201' on Google Earth which will place you about 4 miles west of the deposit. A shallow prospect pit was dug in vermiculite prior to 1944. Only a very small amount of vermiculite was found. The vermiculite contains chlorite, kyanite and corundum. Samples of vermiculite-chlorite-biotite-corundum schist collected from a small prospect pit contained as much as 10-20% corundum. A minor amount of corundum is gem quality. Several specimens produced high-quality ruby and pink sapphire.
Cordierite was discovered in nearby quartzofeldspathic gneiss. Samples of cordierite gneiss yielded transparent cordierite grains including several weighing >100 carats. Some gneiss collected from the property contained as much as 20% transparent cordierite. The cordierite occurs as rounded to disseminated grains and large nodules. Foliation in the host rock parallels the margin of nodules and in some samples appears to terminate against the nodule boundary, suggesting that some of the cordierite formed during a post regional metamorphic event. Nearby, kyanite schist contains 20 to 50% excellent, light to sky blue with lesser tawny, green & red gem-quality kyanite prisms.
Transparent blue iolite was found as large porphyroblasts, nodules & disseminated grains in gneiss adjacent to corundum and kyanite schist. The iolite was traced over a strike length of 500 feet and continues under soil for an unknown distance. A handful of large nodules were found at the time of discovery that include a raw, high-quality transparent gem known as the ‘Palmer Canyon Blue Star’ of 342.8 grams (1,714 carats), which was the largest iolite gemstone in the world at time of discovery. In addition to clear, transparent, violet blue gem-quality cordierite, some black translucent cordierite (Palmer Canyon Black) was recovered. The Palmer Canyon Black produces attractive cabochons and faceted stones. Palmer Canyon Black gemstones of 4 to 6 carats were faceted in Sri Lanka. At least 10 different categories of gems were described at Palmer Canyon.
Much of the high quality rough material ranges from pleasing violet to a very light-blue color with only a hint of cleavage and parting. Microscopic examination shows a few mineral inclusions in some gems. Gray to dark gray cordierite has well-developed parting and cleavage. A group of cabochons were cut that weighed 0.27 to 3.02 carats. These were dark-gray to black, translucent to opaque, near gems with distinct cleavage, parting and fractures.
Two poor quality specimens were also faceted that yielded a 3.9-carat lozenge-cut stone and a 3.4-carat marquise. Both were flawed with visible cleavage and parting. However, both produced surprisingly attractive jewelry when mounted in necklaces. Some bluish gray to gray translucent to cloudy material represents rehealed mylonitic cordierite that is poor-quality
This is one of the greatest gem discoveries in the US. Grizzly Creek was accessed from the Palmer Canyon road about 4 miles east of the Palmer Canyon deposit at the base of the Laramie Range. To fly to this deposit, fly to 'Grizzly Creek, Rock River, WY' on Google Earth.
Following discovery of Palmer Canyon, similar deposits were predicted to exist in Grizzly Creek (Hausel and Sutherland, 2000). The thermal metamorphic event responsible for the large cordierite porphyroblasts at Palmer Canyon appears to have been widespread in the central portion of the Laramie Range. The earlier prograde metamorphic event produced large prophyroblasts of kyanite in the adjacent rocks.
It became clear during the initial field investigation that a major gem deposit had been discovered. Very large masses of gem-quality iolite were found, as well as large quantities of gem-grade kyanite. Cordierite at Grizzly Creek is surrounded by kyanite and sillimanite schists that contain minor corundum. The kyanite and sillimanite schist lies in a 300 by 5000 foot belt of metapelite. Much kyanite appears to be cabochon grade and has a very pleasing, sky-blue color, with some tawny and pink specimens.
The iolite is massive & forms large replacements of the schist. This one deposit may represent the largest iolite occurrence in the world. During reconnaissance, specimens of massive iolite were collected including one football-size transparent gemstone that weighed 24,150 carats the largest iolite gem found in the world. It now resides in the Wyoming Geological Survey museum. However, this stone is dwarfed by masses of material that remain in place in Grizzly Creek. Some of the massive gem material will require quarrying operations to recover. It is very likely that gem specimens >1 ton (>4.5 million carats) could be recovered! In outcrop, the iolite is weakly iron stained on the surface and shows excellent light blue color & transparency on fresh surfaces. It is not known how much if any of this material has been destroyed by mylonitization (deformation). For example, several specimens collected at Palmer Canyon showed distinct mylonitic to ultramylonitic texture in thin section that resulted in a cloudy, light-blue and glassy material of poor quality.
Sherman Hills-Ragged Top
The first report of iolite in Wyoming was by Sinkankas (1959). A brief description indicated that iolite was a widespread constituent of schist & gneiss. In describing a deposit Sinkankas wrote, “one estimate has placed the quantity available at thousands of tons” (remember that a ton contains 4.5 million carats!!!). A couple of specimens I found along the southern edge of the Ragged Top cordierite deposit were glassy broken fragments of rather light blue color, verging towards grayish, small sections are clear and suitable for faceted gems.
Sinkankas also wrote ... "It is entirely possible that important amounts of gem quality material will be produced from this locality in the future.” Unfortunately, Sinkankas did not give a location: the whereabouts of this giant deposit remains unknown?
At the time of writing (1959), only one cordierite deposit had been described in the literature. The deposit, known as the Sherman Mountains deposit 15 miles south of Palmer Canyon. The deposit is in Proterozoic (1.4 Ga) metanorite, syenite and syenite-diorite gneiss of the Laramie anorthosite complex intrude the Cheyenne suture (1.8-1.6 Ga) zone. Widespread lenticular to tabular layers of cordierite is found in metanorite (hypersthene gneiss), gneiss and syenite along the southern margin of the anorthosite complex (1.5 Ga).
The host rock is described to have 50-80% cordierite. The occurrence lies 0.5-mile west of Ragged Top Mountain in a belt 0.3 to 1.2 miles (0.5-1.9 km) wide & 6 miles (9.6 km) long. The host gneiss is highly foliated, intensely folded and contorted. The weathered cordierite was described to have dark brown surfaces that yield to blue or bluish gray massive material on fresh surfaces. I was able to obtain small samples of disseminated cordierite along the margin of this deposit. All of the cordierite was very high-quality gem material. Massive portions of this deposit remain unevaluated for gems and may represent the largest, colored gem deposit in the world. This is likely the same deposit described by Sinkankas.
The deposit is described to be scattered over a few square miles in lenticular to tabular masses in low ridges of metanorite 5 miles long and 0.25 to 1 mile wide. Some exposures are described as having 60 to 80% cordierite. It was estimated that the combined deposits with strike lengths of 100 feet or more, contained >453,600 tonnes of cordierite In other words, a potential resource of 2.27 trillion carats!
Sinkankas (personal communication, 2002) indicated that much of the material was gem-quality (Sinkankas, 1959, 1964). This (along with Grizzly Creek) could be one of the greatest discoveries of colored gemstones. To visit this deposit from your computer, fly to: 'Ragged Top Mountain, East Albany, WY 82072' on Google Earth. While you are in the area looking at the foliated anorthosite-syenite complex, note that iolites are scattered over this area and to the southwest is a distinct group of lakes that line up (structurally controlled) with what may be some carbonate salts in the soils. These are great candidates for undiscovered diamond deposits that are known as the Horse Creek Lakes cryptovolcanic structures.
Another iolite deposit in the northern Laramie Mountains is referred to as Owen Creek (Hausel, 2009). This contains kyanite, sillimanite, cordierite & relict staurolite in pelitic schist & remains unexplored. Cordierite is also reported at South Pass (Hausel, 1991), Copper Mountain (Hausel and others, 1985), in the Sierra Madre, and in the Powder River Basin. The cordierite occurrences at South Pass were investigated by me during field mapping of the greenstone belt. I did not observe any gem-quality material there. However, I highly recommend investigations of cordierite at Copper Mountain as this supracrustal belt contains abundant metapelite (alumina-rich rock) that was subjected to similar metamorphic conditions as the Elmer?s Rock greenstone belt. For more information, see Hausel (2009a, 2009b, 2009c).
How To Find Iolite
First you need to take me (just kidding). I love to hunt gemstones & I have a nose for finding iolite.
Iolite is found in amphibolite-grade metapelites (mica rich rocks). Typically it occurs where the rocks have been subjected to high pressures & temperatures that reached the alumino-silicate triple point (nearby rocks contain kyanite, sillimanite & andalusite). It is also found as a replacement mineral in some syenites and anorthosites. Few people know how to recognize this gem.
What I found is not only the largest gemstones, but also the largest colored gem deposits in the world. You would think that this would attract some interest. Visualize this. Iolite sells for about $25 to $125 per faceted stone. It can be faceted for about $0.50 a carat. Gems of iolite larger than 12 carats are unheard of on the world market. It doesn't take a nuclear physicist to see the potential here.
And there are likely more iolite deposits in this region. But someone has to look. And after billions of carats of the gem have already been identified, it will take the legislature with its deep pockets to finance research into marketing, mining and cutting the gem material in Wyoming.