Finding Gemstones - A Prospector's Guide

"Who can find a virtuous woman? for her price is far above rubies" Proverbs 31:10

[Updated, 2/8/2022]. One of great gemstone discoveries in Wyoming occurred near the turn of the 20th century when iolite was discovered in the central Laramie Mountains (Hausel, 2014). While searching for another gemstone, the author came across the first of a group of iolite deposits in the Laramie Mountains (Hausel, 2002). At the time of discovery in 1996, the author was exploring a vermiculite schist for gem rubies and sapphires west of Wheatland, when a small specimen of flawless, gem-quality iolite was spotted in dirt south of the ‘Rolf’ vermiculite-corundum prospect. Over the next few hours, the author recovered several detrital specimens of gem-quality iolite and located the outcrop (lode) containing the gemstones.

A nearly fist-size, gem-quality, 1,714-ct, iolite nodule collected by the author at Palmer Canyon in
the Laramie Range, Wyoming. Note the presence of a thin reaction rim at the right side of photo
consisting primarily of green mica. Dimensions of this specimen is approximately 3 by 4.5 inches.

After finding a small specimen of detrital iolite sitting in dirt in a two-track road, more detrital stones were discovered while searching for the source rock. After some time, iolite was found in outcrop as disguised grains coated by pinite, a reaction rim coating the iolite. Additionally, essentially all of the iolite gneiss was buried under a thin layer of soil. East of the discovery site, more iolite was found in the gneiss by breaking the gneiss with a sledgehammer. In addition to the flawless ‘Palmer Canyon Blue Star’, other specimens weighing a carat to several hundred carats were recovered: most gem quality.

Extraordinary color in this 12-carat faceted ruby from Palmer
Canyon, Wyoming.

Following announcement of the discovery, a prospector from Colorado filed a claim on the discovery and dug a trench with a backhoe. After unsuccessfully trying to find the outcrop on three different occasions, the author flagged the outcrop for the prospector, but the prospector still could not find the deposit. Finally the labeled the outcrop with flagging tape and placed a sample of iolite in a sample bag with a note ‘Dig Here!’ The prospector still missed the iolite. Apparently he was avoiding the gneiss in order to dig in soft soil. The author finally met the prospector and his partner in the field to point out the outcrop. When the prospector trenched across the gneiss, a few hundred thousand carats of iolite were exposed in about a cubic yard of material!

Iolite cross with gold and diamonds.

Much of the iolite and rock from the trench was ultramylonite (intensely sheared and granulated rock) in which the gem value of the iolite had been destroyed by tectonic grinding and crushing along a shear zone (fault). To the west at the original discovery site, this did not appear to be a problem. The author recovered a few hundred carats of very high-quality gem material from the backhoe trench as well as many large, high-quality gemstones at the original discovery site at west end. Some faceted material from the backhoe pile produced eight gems (8 to 12 carats) (Vic Norris, personal communication). So, if it was this hard to find the Palmer Canyon host rock, it should provide an indication the region likely hides more gem deposits. The presence of favorable host rocks (aluminum-rich mica schists) that have been subjected to triple point amphibolite-grade metamorphism, suggests this region of the central Laramie Mountains will likely host more iolite gemstone deposits as well as a very good potential for more ruby, sapphire and kyanite gemstones and a good possibility for other gems such as garnet, sillimanite, andalusite, and staurolite. 

The Palmer Canyon discovery was followed by discovery of a world-class iolite deposit four miles southwest in Grizzly Creek in 2004 which included the largest iolites found on earth. This was followed by yet another iolite discovery near the Sherman Mountains in 2005 which could host the largest colored gemstone deposit ever found (Hausel, 2005, 2005a); however field investigations are needed to verify size, extent and quality of gemstones as only cursory field studies and reconnaissance were completed and only a small portion of terrain surrounding the discoveries was ever explored for gemstones. This and all other pragmatic projects was terminated by the state geologist. These discoveries could have resulted in a new industries for Wyoming which could have yielded jobs, wages, severance taxes and royalties.

A thin slice of fractured iolite from Wyoming.

Gemologists refer to the cordierite [(Mg,Fe3+)2Al4Si5O18] as iolite; but, geologists and mineralogists prefer the term ‘cordierite’. The mineral has also been called dichroite and water sapphire although these are less commonly used. 

Cordierite is often found in the vicinity of other alumino-silicate porphyroblasts (large metamorphic minerals composed primarily of aluminum and silica) such as andalusite, kyanite, staurolite and sillimanite. Iolite host rocks include alumina-rich schist (metapelite) and gneiss that have considerable mica and have been subjected to amphibolite-facies metamorphism. Amphibolite facies refers to a general range of pressure and temperature applied to rocks during recrystallization at depth. Cordierite has also been described as a replacement mineral in alumina-rich syenite-anorthosite complexes (such as the Laramie Anorthosite complex) and in shale (Kievlenko, 2003). It is noteworthy that south of Palmer Canyon and Grizzly Creek, a 350 mi2 syenite-anorthosite batholith complex crops out in the Laramie Mountains and potentially hosts the largest iolite deposit on earth. And it is likely other iolite deposits will be found in Wyoming – particularly in the central Laramie Mountains, the northern Laramie Mountains and possibly the Copper Mountain district of the Owl Creek Mountains.

Large pseudo hexagonal nodule in cordierite gneiss, Palmer Canyon, Wyoming 

Well-crystallized cordierite forms short prismatic pseudo-hexagonal crystals (six-sided) with rectangular cross sections as well as the more common form of compact, granular masses and nodules that have no obvious crystal form and found in various shades of blue, bluish-violet, gray or brown. Fresh cordierite has a hardness of 7 to 7.5 and specific gravity of 2.55 to 2.75. This hardness is favorable for durable gemstones. 

Iolite is as hard as quartz and harder than glass and tanzanite. But the specific gravity of cordierite is unfavorable for placer concentration. With this in mind, it is surprising most iolite on the market today is recovered as a by-product of placer mining in Sri Lanka. Since there is a lack of a continuous supply of iolite, it is difficult to find the gemstone in jewelry stores although it is marketed on TV. A steady supply of the gem with creative marketing strategy could result in an iolite industry rivaling tanzanite. But currently, there is no steady supply, and the gem remains greatly undervalued. To get an idea of how attractive the faceted gemstone is, it is recommended to search the internet for photos of faceted iolite. 

Iolite exhibits distinct pleochroism. Pleochroism in iolite results in color change from light gray, dark violet-blue, to light sapphire blue as the mineral is rotated in light. Pleochroism is pronounced in transparent specimens such that the gem will appear deep blue when viewed down the c-axis of the mineral and light-blue to light grey-blue in other orientations (Hurlbut and Switzer, 1979). These color variations are one of the attractive features of the gem and also a physical characteristic used to identify the mineral.

A flawless, several hundred carat xenoblast iolite in Palmer Canyon Gneiss.

Iolite is often coated by pinite, a reaction rim of tiny muscovite, biotite and chlorite mica that can cloak the blue gem material (Dana and Ford, 1949). Much iolite recovered at Palmer Canyon was partially altered to pinite (Hausel, 2002). Pinite is light-green due to abundant chlorite (see top photo of Palmer Canyon blue star gemstone). These pinite reaction rims coating specimens at Palmer Canyon are typically about a millimeter thick. The coating is a result of unstable conditions during the final phase of recrystallization during metamorphism. In Grizzly Creek, some iolite was later altered to limonite (FeOH) during weathering suggesting iolite in Grizzly Creek is more iron-rich than the magnesium-rich iolite at Palmer Canyon.

Transparent iolite is suitable for gems as are some translucent to opaque varieties. The luster of iolite is vitreous and when polished should become increasingly lustrous. Iolite of highest demand is deep, bright, vivid sapphire blue, although very light blue transparent gems are also very attractive. One uncommon variety of iolite reported outside of Wyoming has mineral inclusions of hematite that produces reddish aventurescence known as ‘bloodshot iolite’. Other inclusions may produce cat's eye or asterism in cabochons – none of which has yet been recognized in the Wyoming iolites, but could occur. Many Wyoming iolites have tiny mineral inclusions of mica. 

Beautiful Wyoming iolite in silver for sale on the
internet.

Iolite is a low-priced gem. Faceted gems less than 5 carats are usually less than $200/carat and may be as low as $50/carat for good, one carat stones. Gems of 5 to 10 carats can be valued in the hundreds of dollars per carat and flawless faceted stones in the range of 10 to 12 carats may be valued at more than a thousand dollars. Gemstones of more than 12 carats are unheard of on the market, but common in the Wyoming deposits. Rough material collected at Palmer Canyon and Grizzly Creek includes some of the largest iolite gems ever found: more than a dozen stones recovered by Hausel were heavier than 100 carats, with some heavier than 1,000 carats, while a few are heavier than 10,000 carats. Some gemstones left in outcrop at Grizzly Creek were estimated to be heavier than 100,000 carats! 

Iolite crystallizes in the orthorhombic crystal system and when well crystallized, cordierite occurs as pseudohexagonal prismatic twins but most often found as rounded porphyroblasts. It has common parting and fair cleavage. Being brittle, it yields sub­conchoidal fracture and resembles quartz or sapphire but can be distinguished from both by pleochroism and subconcoidal fracture. It is also distinguished from sapphire by hardness. Sapphire is harder.

Geology & Genesis of Iolite. Cordierite is formed by metasomatic processes but is stable over a considerable temperature range. In other words, the mineral replaces existing minerals with the assistance of reactive hydrothermal fluids with favorable chemistry. It is also formed by recrystallization of other minerals during metamorphism. The gemstone has been found as porphyroblasts (large crystals mixed with smaller crystals) and xenoblasts (coarse-grained rounded to nodular crystals) in some schists and gneisses, as replacement minerals in anorthosite-syenites, in vitrified sandstones in contact with basalt, and in shales altered by burning coal seams (Dana and Ford, 1949). This means that clinker deposits in Wyoming and Montana should be prospected for iolite as there is considerable clinker in the Powder River Basin. In the geological past, many coal seams at or near the earth’s surface burned worldwide as a result of spontaneous combustion and lightning strikes. The burning coal released considerable carbon monoxide, ash, carbon dioxide and other pollutants and was hot enough to melt adjacent shales to form clinker – a porous baked rock that looks similar to some volcanic rocks. On your journey to Gillette, Wyoming, look for red clinker along the highway that looks like a volcanic rock. 

Iolite porphyroblast (large crystal) in iolite gneiss, Wyoming.

Cordierite may also be found in the same rocks that contain other porphyroblasts such as sillimanite, kyanite, andalusite, biotite and/or spinel. In low- to moderate-grade metamorphosed schist (rock recrystallized at relatively low to moderate pressures and temperatures), cordierite porphyroblasts may occur in a groundmass of quartz, sillimanite, muscovite and cordierite. In other words, it may be found as large, massive, nodular crystals in a fine-grained rock matrix. In high-grade metamorphic rocks (rocks crystallized at high pressure and temperature) cordierite may show pseudo-hexagonal crystal habit. 

Cordierite may also form as a result of chloritization (i.e., it may be produced during replacement of host rocks by dark-green chlorite mica). In silica-deficient rocks (those with low silica content), it may be associated with corundum, spinel and alkali feldspar. In thermally altered rock, cordierite and corundum are incompatible and react to produce spinel and sillimanite (Deer and others, 1972; Spry, 1969). Where found, cordierite gneiss should lack garnet, since garnet and muscovite react under high pressure and temperature to produce cordierite, potassium feldspar and spinel during metamorphism.

A 12-carat raw pink sapphire from Palmer Canyon - specimen
from the Vic Norris collection.

Iolite is found in Canada, India, Myanmar (Burma), Sri Lanka, Brazil, Tanzania, Finland, Germany, Norway, Greenland and the United States. The principal source for the gemstone is Sri Lanka, where miners periodically find iolite pebbles in placers. Being that the gemstone is recovered as a secondary product with other gemstones, there is not a steady supply of the gemstone to jewelers.

In Wyoming, iolite has been identified in three lode deposits in Archean gneiss (>2.5 billion years) known as Palmer Canyon, Grizzly Creek and Owen Creek. A fourth deposit was recognized in the Proterozoic age Laramie syenite-anorthosite complex (~1.5 billion years old) known as the Sherman Mountains deposit. This later deposit could potentially be an enormous, disseminated to massive gem deposit based on past descriptions of the deposit and could potentially host more than 2 trillion carats of gemstones (Hausel 2002, 2004, 2006a)! Two of the other deposits (Palmer Canyon and Grizzly Creek) are poly-gem occurrences with associated gem-quality kyanite, ruby and sapphire. The Sherman Mountains deposit remains unexplored for gems even it could potentially be the largest colored gemstone deposit in the world (Hausel, 2006a). 

Palmer Canyon (N/2 NW Section 18, T24N, R70W) (42°3'25"N; 105°17'10"W) (recommended: Reese 1:24,000 scale topographical map (see Topoquest) and Laramie Peak 1:100,000 topo map). Plot the approximate location of the Palmer Canyon deposit on a copy of the Reese 1:24,000 scale topographic map using the first set of coordinates in the parentheses above. This will place you in the north-half of the northwest quarter of section 18, T24N, R70W adjacent to the Palmer Canyon Road. Look for the ‘T’ in ‘FOREST’ on the map in this section: the deposit lies just above the ‘T’ in a white area on the map. It is up to the reader to obtain permission for access. Remember, it is illegal to trespass on private property and to take minerals from a legal mining claim. 

Generalized map of Wyoming showing location of
Palmer Canyon

Use the GPS coordinates in the second set of parentheses (above) to view the deposit on Google Earth. Now you should have an aerial view of the deposit.

The deposit lies on a ridge along the southern flank of Palmer Canyon 17 miles west of Wheatland. Iolite occurs in a succession of Archean quartzofeldspathic gneiss, granite gneiss, metapelite, and biotite-chlorite-vermiculite schist north of the Elmer’s Rock greenstone belt. The deposit is accessible from the Palmer Canyon road which is paved to the forest boundary from Wheatland. The deposit lies a short distance further west (in less than a mile) along the Palmer Canyon road and is just north of the road along a short jeep trail running east of the main road.

What first attracted the author's attention to this deposit was a large rock sitting in the basement of the Wyoming Geological Survey building on the University of Wyoming campus. The rock was biotite-phlogopite vermiculite schist containing several small ruby and sapphire crystals in the matrix. There was no identification on the rock, but the author suspected it had been picked up by one of the other staff geologists at the Wyoming Geological Survey, the late Ray Harris, simply because only Ray and the author ever did any field work at the Survey. Harris was working on a project on decorative stones and had been attracting considerable interest with his work until the administration shut him down by taking away his field vehicle. 

Gem kyanite from the Central Laramie Mountains.

Anyway, the author stopped into Harris's office to get information on the rock. He asked if the rock was his and what he thought about the garnets (we should use the term boulder because Harris never took small samples) and indicated he was quite impressed by the garnets. Hausel asked where he collected the rock. 

It took a few days but Harris finally found a field note on the locality and said it came from the Rolf vermiculite prospect west of Wheatland. The author then asked Harris if he had noticed the garnets had distinct parting (garnets do not have parting). Harris indicated he had, but wasn't sure why. The author further asked, “Did you see that the garnets were hexagonal instead of isometric?” At this point, the author quit toying with him and pointed out the rock was filled with rubies (corundum) and not garnet. One cannot fault Ray for not recognizing this mineral because gemstones are rarely discussed in college and few geologists ever get the opportunity to see rough gemstones during their college careers - a major shortcoming of the university educational system. 

Ruby-kyanite vermiculite schist from
Palmer Canyon

In the 1930s and 40s, vermiculite was sought for use in fire-resistant insulation. Hagner (1944) investigated vermiculite deposits throughout Wyoming and published a short paper on the known deposits. At the location in Palmer Canyon, a shallow prospect pit was dug about 4 feet deep on vermiculite schist (glimmerite) at what is known as the Rolf prospect. Only a very small amount of vermiculite was exposed at the surface which had considerable corundum and some kyanite. After some research, The author noted the association of vermiculite and corundum (both are aluminum-rich and silica poor) and decided to investigate other vermiculite deposits and discovered five more ruby deposits in Wyoming. So, if you have any publications on vermiculite in your state, province or country, you might visit those deposits and search for ruby and sapphire.

“Search aluminum-rich rock such as vermiculite, as there is a close association of vermiculite with ruby and pink sapphire”.

Pink corundum (sapphire) vermiculite schist from
Palmer Canyon

Hagner (1944) interpreted vermiculite schist to form by replacement of biotite by hot pegmatitic fluids. Pegmatite is not found in the immediate area, so possibly hot fluids were driven off other rocks during regional metamorphism. Cordierite was not mentioned in Hagner’s report and there was no appraisal or description of corundum. 

Some samples collected from the schist by Hausel contained 2 to 20% corundum! Some corundum was gem quality and included white and pink sapphire and a few red rubies: some were cabochon grade and a few were facet grade. 

At Palmer Canyon, cordierite forms rounded to disseminated grains and large nodules: a few are inter grown with quartz. Foliation in the host rock parallels margins of nodules and in some samples terminates against nodules suggesting cordierite formed during a late metamorphic event. Kyanite and sillimanite may be present in the host rock with cordierite, but only as minor to accessory components. Some secondary calcite crusts some surfaces. 

Palmer Canyon is underlain by intercalated gneiss and schist with near vertical foliation and a N80°W trend. No exploration has taken place at depth; thus a cache of gemstones could lie at any depth. The quartzofeldspathic gneiss is the primary host for cordierite and samples contain 5 to 50% light to sky blue kyanite. 

Close up view of faceted gems sitting on the iolite
porphyroblast.

The following types of gems, near-gems and potential gem material were described at Palmer Canyon by the author: (1) high-quality flawless violet-blue, dark-blue to light-blue transparent iolite, (2) dark-gray to dark-blue transparent iolite with tiny mineral inclusions, (3) black translucent iolite, (4) low quality, dark-gray to blue-gray translucent to cloudy mylonitic cordierite (mylonite is intensely sheared and crushed), (5) red transparent ruby, (6) red translucent ruby, (7) reddish-brown translucent sapphire, (8) white to pink sapphire, (9) sky-blue translucent kyanite, and (10) common translucent cordierite with rhombohedral fractures.

It is interesting that a group of gemstones from Palmer Canyon were dressed in gold necklaces and offered to a group of women in Fort. Collins, Colorado at no cost. The gem of choice was the 3.4 carat rhombohedral fractured blue iolite (top photo to the right). This was chosen over a flawless transparent iolite and a near flawless, transparent ruby (photos courtesy of Chuck Mabarak). 

The iolite host was traced over a strike length of 500 feet and likely continues under soil for an unknown distance at both ends of the mapped area. A handful of large nodules were found during field investigation along with the ‘Palmer Canyon Blue Star’. In addition to clear, transparent, violet-blue gem-quality cordierite, some black translucent cordierite (‘Palmer Canyon Black’) was recovered. The Palmer Canyon Black is all cabochon grade. 

Much high-quality iolite rough ranges from pleasing dark blue, to violet to very light-blue color sometimes with a hint of cleavage and parting. Mineral inclusions for the most part are invisible to the naked eye although some larger inclusions are visible and form white acicular grains (possibly sillimanite) and distinct pseudo-hexagonal black biotite. 

Gray to dark gray cordierite is translucent with well-developed parting parallel to the c{001} axis and cleavage along b{010} axis. Many specimens exhibit rectangular cross sections and a few have pseudo-hexagonal habit. A group of cabochons cut from this material weighed 0.27 to 3.02 carats. These were dark-gray to black with distinct cleavage, parting and fractures. 

References Cited 

1.0 carat Palmer Canyon iolites

• Dana, E.S., and Ford, W.E., 1932, A Textbook of Mineralogy, John Wiley and Sons, New York, 851 p.
• Deer, W.A., Howie, R.A., and Zussman, J., 1972, Rock-Forming Minerals – vol. 1 Ortho-and Ring Silicates. William Clowes & Sons, Ltd. New York, NY, 333 p.
• Hagner, A.F., 1944, Wyoming Vermiculite Deposits: Wyoming State Geological Survey Bulletin 34, 47 p
• Hausel, W.D., 2002, A new source of gem-quality cordierite and corundum in the Laramie Range of Southeastern Wyoming: Rocks & Minerals v. 76, no. 5, p. 334-339. 
• Hausel, W.D., 2004, Geological Reconnaissance of the Grizzly Creek Gemstone Deposit, Laramie Mountains, Wyoming – A Potential Source for Iolite, Sapphire, Ruby & Kyanite: WSGS Open File Report 04-14, 8 p.
• Hausel, W.D., 2005, Geologists Locate Giant Gemstones: ICMJ Prospecting and Mining Journal, v. 74, no. 7, p. 7-9. 
• Hausel, W.D., 2005a, Minerals and Rocks of Wyoming – A Guide for Collectors, Prospectors and Rock Hounds: Wyoming Geological Survey Bulletin 72, 159 p. 
• Hausel, W.D., 2006a, Gemstone discoveries in Wyoming: Rocky Mountain Association of Geologists Outcrop 55:3.
• Hausel, W.D., 2014, Finding Gemstones - A Prospector's Guide to Gemstones, Gold, Rocks & Minerals: Gemhunter Publications, 368 p. 
• Hausel, W.D., and Sutherland, W.M., 2000, Gemstones and Other Unique Minerals and Rocks of Wyoming - A Field Guide for Collectors: Wyoming State Geological Survey Bulletin 71, 268 p.
• Hurlbut, C.S., Jr., and Switzer, G.S., 1979, Gemology: John Wiley and Sons, New York, 243 p. 
• Kievlenko, E.Y. 2003. Geology of Gems. Ocean Publications Ltd., Littleton, CO. 432 p.
• Spry, A., 1969, Metamorphic Textures. Pergamon Press, Oxford, England, 350 p.

Two 4- and 6-carat faceted Palmer Canyon Black iolites 

Close up of iolite gemstone collected by the author at Grizzly Creek. This stone weighed several
thousands of carats!

A 6-carat iolite from Palmer Canyon

A 16-carat iolite from Wyoming

Group of 6 to 12 carat iolites from Wyoming

A 10-carat Palmer Canyon black cabochon

A 100+ Carat iolite from Palmer Canyon collected by Hausel

Close up of large iolite porphyroblast collected by Hausel at Palmer Canyon

Outcrop of massive iolite discovered at Grizzly Creek Wyoming by the author.
Essentially, everything in this photo with the exception of the rock hammer and 
milky quartz vein cutting through the iolite, is one, big massive polite gemstone!

Wayne Sutherland sits in front of massive iolite outcrop at Grizzly Creek, Wyoming.
This is a very sizable outcrop and likely hosts more than a million + carats of the
gemstone. With the exception of the quartz vein above Wayne's back pack, nearly
all of the remaining outcrop in the photo is iolite.