How to Identify Diamonds in Nature

14.2 carat octahedral diamond from
Kelsey Lake, Colorado (photo
courtesy of Howard Coopersmith).

In addition to the type of diamond we see at weddings, other varieties of extremely hard natural carbon are known including carbonado (polycrystalline) and lonsdaleite (hexagonal). These are all forms of carbon, as is graphite. But carbonado and lonsdaleite are very rare compared to natural diamond (which in itself is very rare). For information on lonsdaleite and other natural forms of hard carbon, refer to Erlich and Hausel (2002). Only crystalline, isometric diamond (the kind of diamonds we buy from jewelry stores) will be considered.

In its simplest form, isometric diamond is an equal-dimensional mineral that may form six-sided crystals known to mineralogists as hexahedrons; but to prospectors, these are simply cubes. A more common habit (form) of diamond is the octahedron. To imagine what an octahedron looks like, visualize an Egyptian pyramid. Now imagine that pyramid surrounded by a crystal clear lake with its refection in the water. It would appear as if two pyramids were attached at the base: this would be an eight-sided octahedron.



Modified octahedron with many more faces.

Many octahedral crystals develop ridges on the octahedral faces resulting in crystals of trisoctahedral or hexoctahedral habit. Partial resorption of octahedral diamonds produce rounded dodecahedrons (12-sided crystals) with rhombic faces. Many dodecahedrons have ridges on the rhombic faces resulting in a 24-sided crystal known as a trishexahedron. Four-sided tetrahedral diamonds are sometimes encountered that are thought to be distorted octahedrons. Another relatively common form of diamond is a macle, or twinned diamond. Diamond macles appear as flattened triangular crystals. It should be obvious that diamonds have many crystal habits, so if you would like to know more about these, it is recommended to read Bauer (1968a) and Bruton (1978).



Most diamond surfaces will have growth trigons (equilateral triangles) and less commonly trigonal pits. And some will have hexagons (6-sided pits or raised areas. You are likely getting the idea that there are many complexities to understanding diamond crystal habits or shapes. But don’t despair. If the above information snowed you, just remember there is a simple instrument known as a diamond detector sometimes called a diamond detective that you can purchase on-line for a minimal price. It will tell you if you have a diamond or not by simply touching the crystal and pressing a button. Nothing could be simpler for a prospector, rock hound and even geologist and gemologist.

Magnified diamond surface showing several trigons.

Diamonds have distinct, brilliant, greasy luster that is likened to oiled glass. Often quartz is mistaken for diamond, but the dull luster of quartz is no match for the brilliant adamantine luster of diamond. Gem-quality diamonds can be translucent to transparent, colorless, green, yellow, brown, black and rarely blue or pink. Opaque and heavily included diamonds (bort) are used for industrial purposes and have little value.

Diamond is brittle, extremely hard (H=10 on the Moh’s scale), with a specific gravity of 3.5, and has perfect octahedral cleavage. Even though diamond is heavier than water, it is non-wettable (hydrophobic) and will float on water given the right circumstances. Some flotation devises have been designed to extract diamond using water’s surface tension. Being hydrophobic, diamonds are also grease attractive. This property is used to recover diamonds in many places around the world, where shaking tables are coated with grease to extract diamonds from concentrates run over grease tables with water. The grease, usually a mixture of Vaseline and paraffin in a 10:1 ratio, is coated on the shaking table surface.

Under ultraviolet light, many diamonds fluoresce pale blue, green yellow, and rarely red. This characteristic of diamond is used in many diamond mills, such as Sortex, which detects fluorescence from diamonds when they are x-rayed.

Since diamonds are extremely rare, it takes considerable effort and patience to find the gemstone. It has been estimated diamond occurs in concentrations of less than 1 part per million in commercial diamondiferous kimberlites. This means you have 999,999 parts of waste rock to run through to find that 1 part per million diamond only after you have searched and searched for the primary host rock. And not all kimberlites, lamproites and lamprophyres have diamond.



Sloan kimberlite, Colorado. This kimberlite has diamonds as
well as other gemstones including Cape Ruby (pyrope garnet)
and chromian diopside.

Years ago, it was common knowledge in the mining industry that only about 10% of kimberlites contained diamond (Lampietti and Sutherland, 1978; Hausel, 1998). This estimate was not quite correct as many other rocks at the time had been erroneously classified as kimberlite – and over the years, there has been a lot more kimberlites found (Hausel, 2008a). So the percentage of diamondiferous verses barren kimberlites is much higher than originally thought. But at the same time, the percentage ofdiamondiferous verses barren lamproites and lamprophyres is very low.



Iron Mountain kimberlite, Wyoming

The primary rocks that diamond is found in are known as peridotite and eclogite. These are rare mantle-derived rocks (nodules) that are actually sampled, or picked up by rare volcanic eruptions (i.e., kimberlite, lamproite and some lamprophyre). Thus the kimberlite, lamproite and lamprophyre magmas accidentally pick up these rare diamond-rich rocks at great depth and bring them to the earth’s surface in rare old volcanoes. Many of the diamond-rich nodules survive intact after being shot out of the earth’s mantle from depths of 90 to 120 miles, while others break up with their diamonds being diluted in the magma. As an example of how rich some primary host rocks are, one sample of eclogite from the Sloan kimberlite in Colorado contained an estimated 20% diamond! But kimberlite magma itself, was many times poorer in diamond than this eclogite.

No other mineral (other than gold) seems to elude correct identification by prospectors and rock hounds. This is because of a poor understanding of mineralogy and because most people tend to see things that don’t exist and let their imaginations run wild. After 30 years of working with the public and identifying samples for people almost on a daily basis, I only had two people who correctly identified diamond. Many hundreds thought they had diamond, but were seeing things that were just not there.



I have many stories about these prospectors and rock hounds that are both educational and interesting. One prospector called me from his truck at Jeffrey City and wanted to know what to do with all of the diamonds he had found. I was impressed: 

"How many did you find?" I asked.

"There are thousands all over the hill side!" He responded.

Being curious, I asked him, “How are you verifying these diamonds?"

"I just scratch the windshield on my truck, and they leave a nice scratch", he responded.

Being a wise ass, I asked, "Are you going to be able to see out your window well enough to drive home?"



He was right, diamonds will scratch windshields! Windshields are made of glass with a hardness of only 5.5 to 6 on the Moh's scale. This means many minerals will scratch windshields including pyrite, feldspar, corundum and of course quartz. One way windshield’s become pitted (scratched) during dust storms is due to all of the fine sand that is blown into the windshield.

A fairly inexpensive design for a grease table constructed by Jay Roberts at
the Wyoming Geological Survey. The light-bluish white coating is the grease
mixture. The problem with this material (particularly on a university campus)
was that we had to buy Vaseline by the case. We often received accusing
expressions from drug store employees assuming we were with a fraternity
planning for some weekend orgy.

Another prospector called and said he had been diamond hunting for years and never found any. After talking awhile he mentioned his method for diamond testing: "I simply put them on an anvil and hit them with a hammer!" He talked about all of the octahedral crystals he had picked up from streams and kimberlites in the Colorado-Wyoming State Line district (where several known diamond deposits occurred) but none were diamonds because they all failed his test!



A giant diamond from Africa - 620 carats in weight. This diamond was actually on display for a
short time at Wiseman's Jewelry in Laramie, where I was able to photograph the
extraordinary stone.

I then explained to him about the difference between hardness and mechanical brittleness and that all diamonds will break when struck by a hammer. You could hear that sound of ... well, it sounded like muffled swearing in the background as he hung up.

In another case, I received a phone call from an individual who claimed to have found the largest diamond in the world just west of Cheyenne. According to an unnamed gemologist from Cheyenne, this crystal was pronounced to be diamond. But the gemologist suggested that before the prospector put it on and purchased a large mansion on the French Riviera, he should visit my office in Laramie for a second opinion.

I gave him directions to my office. It’s about an hour’s drive from Cheyenne, so I was surprised when he and his three family members were knocking on my office door about 30 minutes later. They were apparently anxious to cash in their millions.

The diamond discoverer introduced himself as ‘Jack’ and did not give a last name, and without further hesitation, opened a locked brief case chained to his wrist and showed me the ‘Star of Cheyenne’. It was fist size - about the same size as the famous Cullinan diamond. The Cullinan was by far the largest diamond ever found and weighed a whopping 3,006 carats and was recovered at the Premier Mine in South Africa. It was priceless and ended up in the Crown Jewels of England.



Kimberlite? Nope, some prospectors would call this kimberlite, but it is
actually a lamproite.

In the late 1970s, I had met Dr. Arnold Waters. Dr. Waters was at the time, the former Chief Geologist for DeBeers in South Africa and he told me that when the Cullinan was found, it had a distinct cleaved surface where part of the diamond had been broken in two during assent to the earth's surface in a kimberlite magma (volcano). He indicated the other half of the diamond could have been as large or larger, but was never found! Did it break off somewhere at great depth and still many miles deep in the earth? Did it make it to the surface and was missed by the sorters and ended up in the crusher where it made many little diamonds? It’s something to wonder about.

The ‘Star of Cheyenne’ was reluctantly handed to me. As soon as I saw it, I knew what it was, but decided to have a little fun. First I showed them how to test a mineral’s specific gravity by weighing the gem in water and then in air. I determined the crystal to have a specific gravity about 2.7 - too light for diamond (diamond's specific gravity at 3.5 is heavy enough it would show up with garnets and black sands in a gold pan). I also tested the hardness by taking a diamond chip and easily scratching a deep notch in the crystal. This resulted in an immediate protest by the family as they thought I was scratching their priceless diamond.

“Hold on!,” I exclaimed. “If this were a diamond, I wouldn’t be able to scratch it with a diamond chip, diamond has a Moh’s hardness of 10 and is the hardest known natural mineral, and it is very, very difficult to scratch a diamond with another diamond”. After I calmed them down and convinced them that they had an ordinary piece of rock crystal (transparent massive quartz), they left the office dejected and drove back to Cheyenne with visions of mansions and Porches fading. And I thought this was over.

The next day, I was contacted by one of our other geologists - Ray Harris (RIP) - who stopped in my office to tell me he had just received a call from a person in Cheyenne who had a probable diamond that he wanted to have verified. The person on the phone explained to him that they had already talked to me, but he and his gemologist decided that another opinion was necessary.

The diamond detective - yep, that's me when I was VP of US Exploration for DiamonEx Ltd,
Australia. During exploration in Colorado, Montana, Kansas and Wyoming, we identified
 hundreds of cryptovolcanic structures that look almost like impact craters with the exception
that these are structurally controlled - located on a fault or similar feature.  You won't be able
to follow me on Facebook, because they lie and make up their own facts - not very scientific.

Ray went back to his office to await the family. I laughed to myself. Ray was a very good geologist, but he had a reputation as a klutz. He was famous for running into things, breaking things, and if anything could go wrong – leave it to Ray. One of my favorite stories about Ray took place at a staff meeting. Ray was holding a cup of coffee in his left hand. I notice this and decided to catch him off guard. So I quickly asked him for the time of day. Without hesitation, Ray rotated his wrist to look at his watch pouring his coffee into his lap. We all had a great time with Ray, but during his last year, he was bullied by his supervisor until he died. I will always miss Ray – he was a good friend.

Prismatic quartz crystal from
Hot Springs Arkansas

Anyway, the Cheyenne family arrived with their gem. They talked about the gemologist’s opinions and their concern about my scratching the diamond. I don't know if Ray had ever seen a diamond in the rough before (few geologists had) and after examining the fist-size specimen with his hand lens, he decided to get a better look at the gemstone and carried it to his microscope in his adjacent lab with the family following him. Then it happened! He lost control of the sample and it crashed onto the floor shattering into dozens of pieces.

Blue quartz from Montana

Ray told me the family turned white as ghosts. But Ray consoled them looking down at all of the pieces. “Well, guess it wasn’t diamond – it has conchoidal fracture”. The family scooped up the fragments of their precious quartz and went home, never to be seen again. When Ray told me about his event – I laughed, and pointed out to him that diamond (as well as quartz) has conchoidal fracture. Ray turned white. But don't worry - it was just a piece of quartz.

Sweetwater agates (quartz) from the
Granite Mountains, Wyoming

Kimberlite Pipes and Volcanoes

Would you like to see a kimberlite pipe erupt? Me too! But don't stand too close. These types of eruptions are very explosive at the point of eruption, and likely have gaseous emplacement temperatures at the freezing point of water and velocities of Mach 3!!!

Below are photos of kimberlites, diamonds, and books written and photographed by the author over the years.

High-wall with exposed diamond-bearing kimberlite breccia at the Kelsey Lake mine, Colorado. If you have Google Earth on your computer, search for 'Kelsey Lake, Colorado' to see the location of the blue ground to see this former diamond mine. Note the large angular rock fragments in the highwall - these indicate there was a tremendous amount of explosive energy during the eruption of this kimberlite pipe (photo by the author).

Diamond-bearing Schaffer kimberlite dike in Wyoming exposed in dozer trench in 1979 or 1980. Jay Roberts, geologist, stands in the trench for scale while I took this photo. The kimberlite is the gray-blue material. The reddish material in the foreground is sheared Proterozoic granite (Sherman granite facies). (photo by the author)

Diamondiferous kimberlite from the Sloan 2 pipe in Colorado. Note the large, rounded pyrope garnet.  The Sloan kimberlites have identified diamond resources and remain mostly untouched. DiamonEx had acquired the Sloan property in 2007 under my direction, but the 2008 economic collapsed took its toll on world diamond prices, the company, and the world. The property was abandoned by DiamonEx, yet it likely still encloses hundreds of $millions in diamonds.

Kimberlite (Devonian) and Granite (1.4 billion years old) contact exposed 
by bull-dozer, Schaffer kimberlite complex, Wyoming. 
Note how sharp the kimberlite contact is and there is no
 evidence that the granite was baked.

Maxwell diamondiferous kimberlite in Colorado - one of many kimberlite pipes and dikes in Colorado and Wyoming that still remains untested for commercial diamonds. Diamonds were recovered from a small sample from this pipe (C.D. Mabarak, personal communication).

Buried kimberlite dike in Wyoming - the kimberlite underlies 
the dirt in the right half of the photo where there appears to be 
thicker and slightly higher vegetation.

Diamonds in the US?  From 'Diamonds and Mantle Source Rocks in the Wyoming Craton' - by W. Dan Hausel, 1998. The diamond-shaped figures represent reported diamonds. The triangles are kimberlite localities (open triangles are diamond-bearing kimberlites), squares are high-pressure volcanics similar to kimberlite, + are lamprophyres and lamproites, the + enclosed by a diamond is diamond-bearing lamproite, the white diamond is the location of the Great 1872 Diamond Hoax site, the dots represent kimberlitic indicator mineral anomalies of note.

Close-up of diamond surface with some of the distinct trigons etched in the 
surface.  Don't know how to identify diamonds? Its not all that difficult. If 
you do not have a background in mineralogy, all you need is the 
Diamond Detector - you can even make your own.

Popular book on diamonds in the US - you might be able to get this at the Wyoming 
Geological Survey at the University of Wyoming.

Book on rocks and minerals that also has brief information on diamonds and on 
kimberlite and lamproite. Available at Amazon

Another popular book on gemstones (and diamonds) that the Wyoming Geological Survey 
forgot to reprint after the current edition was sold out. Photo by Wayne Sutherland.

Gem kyanite from central Laramie Mountains (we found billions of 
carats of this gem - but it remains undeveloped). 
Some of this gem is found with iolite, ruby and sapphire 
in the central Laramie Mountains.

Publications on diamonds from the wyoming geological survey (photo by Wayne Sutherland).

Free download pamphlet on placer diamonds. 

Rough diamond from Wyoming - wow, aren't 
these stones beautiful! Note how the gem has kind of a 
greasy luster. This is characteristic of diamond.

Exploration methods for kimberlite.

Recent publication on geology of the Leucite Hills lamproites and possibilities of diamonds in the Leucite Hills lamproites in Wyoming (may or may not be available at the Wyoming Geological Survey).  I loved working in this area. While conducting research on diamonds, we recovered diamond-stability chromites from some of the lamproites (this suggests the chromites formed under pressures and temperatures similar to that of diamond formation; thus there is a possibility for diamonds in this region).

Essentially all of the projects at the Wyoming Geological Survey were so underfunded, its amazing we found anything. Even though Wyoming rocks may contained diamonds, we were unable to test any material (other than a couple of rocks). Elsewhere in the world, there is a correlation between olivine and diamond content in some lamproites, so I was excited to find a couple of anthills with considerable olivine in the northeastern portion of the Leucite Hills. After looking at some olivine with a hand lens, it was apparent nearly all was gem-quality. So I took the two anthills in sample bags - and Robert Gregory processed the material (no diamonds were found), but we recovered 13,000-carats of gem-quality peridot from this sample!

Diamonds in the world - a 374 page book, but price is too high 

(don't blame me, I receive no royalties for this book, so, unless

you are Elon Musk, personally I would think before buying).

Ruby from Granite Mountains, Wyoming. Specimen
found by Eric Hausel.

Didn't find any diamonds (but lots
and lots of diamondbacks) - nor did
we test material for diamonds. However
the geochemistry of all rocks showed genesis 
 from the diamond-stability field
and a couple of diamonds were
 found in the early 1980s by Cominco American.
Geology of the Iron Mountain kimberlite district.
Another great paper was published as a field trip
guide for the 8th International Kimberlite
conference.

Kimberlite 'diamond' Indicator minerals. These include pyrope garnet, spessartine garnet, pyrope-almandine garnet, emerald-green chromian diopside, picroilmenite (black metallic with white leucoxene crust) and two tiny black, octahedral chromites. Here is an example of how geologists miss gemstones. These were all recovered from the Sloan 2 kimberlite in Colorado when I was working for DiamonEx Ltd. Everyone working in this region for years focused only on the diamonds; yet these are all gemstones and can be faceted into beautiful colored gems while the chromites and picroilmenites could be fashioned into low-value gem cabochons.

Guide to Prospecting and Rock Hunting 
in Wyoming.

There are many gemstones in Wyoming. Most people would have laughed if you told them in 1975 that Wyoming had the greatest variety of gemstones in the US. In 1975, Wyoming had known jade deposits and some agates - but that was about all.

Over three decades, the more I looked, the more I found: dozens of overlooked gemstone deposits and evidence for hundreds more which included commercial gold deposits along with more than 100 gold anomalies.  It was my intention to continue this research along with educating the public to help YOU find gemstones, diamonds and gold using methods I found successful in finding a few hundred mineral deposits.

But morally and ethically, I could no longer work for the Geological Survey or the State of Wyoming, so I moved on. Since 2006, there have been no discoveries of new metal or gemstone deposits.

Need More Information - Check out the Older Posts 

Colorado, Montana, Wyoming - a major diamond province remains overlooked

North American Craton showing position of Wyoming Craton

Aerial photo over Twin Mountain Lake
 anomaly

A few of the Twin Mountain Lakes cryptovolcanic
structures. Note the white carbonate on the
shoreline.

Hundreds of kimberlites, lamproites, lamprophyres, diamonds and cryptovolcanic structures have been identified  in the Wyoming Craton that lies under portions of Colorado, Kansas, Montana and Wyoming. Some of the larger targets were discovered in the Twin Mountains Lake district adjacent to I-80 between Cheyenne and Laramie by the author several years ago, and these remain unexplored. More than 50 cryptovolcanic depressions show structural control, carbonate-rich sediments (in an Archean crystalline terrain) and distinct depressions adjacent (east) of the State Line diamond district. These could potentially be kimberlites with untold amounts of diamonds.

To view these anomalies (some may represent some of the larger diamond pipes in North America) search Google Earth "Twin Mountains, Cheyenne West, WY 82059". I highly recommend that you also examine these on Virtual Earth in the Twin Mountains Lake - Twin Mountains area. 



Some of the first diamonds mined from Wyoming kimberlites within the Colorado-Wyoming
State Line district south of Laramie (photo by the author).

Major Diamond and Colored Gemstone Deposits Found in US

MAJOR DIAMOND PROVINCE DISCOVERED

State Line Kimberlite Province showing locations of (1) Radichal kimberlite &
Mineral Indicator Anomalies, (2) the Iron Mountain kimberlite district, (3) Schaffer,
Aultman, Ferris kimberlites, (4) Keslsey Lake Kimberlites (5) Nix kimberlites, (6)
Sloan kimberlites, (7) Estes park kimberlites, (8) Boulder Kimberlite, (9) Boden
diamond placer. In between these are several hundred cryptovolcanic structures
with similarities to kimberlite pipes as well as more than 300 kimberlitic mineral
anomalies.



False-color aerial photo taken over the Indian Guide district, west of the Iron Mountain kimberlite
 district. The image shows a group of very interesting cryptovolcanic anomalies discovered by the
Wyoming Geological Survey. In total, more than 300 similar cryptovolcanic anomalies and a few
 hundred diamond indicator mineral anomalies were identified in southeastern Wyoming by the
Wyoming Geological Survey, Cominco American, and DiamonEx Ltd. Others were likely identified
by Canadian and South African companies. To date, only 2 of these structures were drilled, the rest
of the anomalies remain untested for kimberlite and diamonds. These anomalies, along with many
kimberlites, lamproites, lamprophyres, diamond indicator minerals, and even placer diamonds found
in Colorado, Kansas, Montana, Utah and Wyoming provide evidence of a major diamond province.

 These cryptovolcanic structures are lake filled (dark to black), with vegetation anomalies (red), and
some surrounding carbonate-rich soil (light-blue bulls eyes), and some are structurally controlled by
distinct lineaments (faults and/or fracture zones). Being these anomalies lie immediately west
of the Iron Mountain kimberlite district and east the Radical kimberlite, it is likely that a few 
anomalies are eroded kimberlite pipes.  Note the roads near these structures to get an idea of scale.

Research suggests that the Wyoming Craton encloses a world-class diamond province as well as major deposits of colored gemstones. The Wyoming Craton includes portions of Colorado, Nebraska, Kansas, Montana, Wyoming, Alberta & Saskatchewan, & encloses the two largest known kimberlite districts in the US & the largest lamproite & lamprophyre fields in North America. Diamonds have been reported in kimberlites and lamprophyres in this craton in Canada, Montana, Wyoming, Colorado and Kansas.

Winkler Crater in Kansas with two trenches dug to sample the material.
Originally classified as an impact crater until it was verified by Doug
Brookins to be kimberlite. Tested by Cominco American in the 1980s
the pipe may have yielded one microdiamond, but there is concern that
the diamond may have been contaminate from the State Line district.

Hundreds of kimberlites, lamproites and lamprophyres were identified over the past few decades. In addition the many known diamondiferous kimberlites & lamprophyres, in recent years, four significant iolite (water sapphire) deposits were found as well as deposits of ruby, sapphire, opal, kyanite gems, jade, chromian diopside (Cape Emerald), pyrope garnet (Cape Ruby), almandine garnet, spessartine garnet, peridot, gem-quality apatite, jasper, agate, onyx and other gems - all found since about 1975. Two of the iolite deposits are world class. This region has turned into an exploration geologists' and rockhounds' paradise.

Hundreds of cryptovolcanic structures were identified by the Wyoming Geological Survey and also by DiamonEx Ltd within this province. Many are quite large and some situated within known diamond districts and within large areas that remain unexplored. In addition to the the known kimberlite, lamproite and lamprophyre districts, more than a dozen new districts containing many cryptovolcanic structures were discovered. As incredible as it seems, a few lie adjacent to interstates and highways and have been missed by millions of travelers every year.

Sloan 5 kimberlite in Colorado - note the exploration pits and also
a distinct structural lineament along the right edge of the open park.
Most kimberlites found in the Colorado-Wyoming province do not
support woody tree growth, and often have a distinct grassy anomaly.
(Photo by the author)

During the past 30 years, the two largest diamondiferous kimberlite districts in the US and the largest field of lamproites in North America were mapped in the Colorado-Wyoming region. Several hundred kimberlitic indicator mineral anomalies were also scattered all over Wyoming, parts of Colorado, Utah, Montana, Kansas and Alberta. Other researchers found similar anomalies.

The several hundred cryptovolcanic structures have characteristics that suggest most are kimberlite pipes. They are circular to elliptical in shape, structurally controlled, many are distinct depressions with distinct vegetation anomalies similar to kimberlites mapped in the past. Some of the depressions are so distinct that they have actually been mistaken as impact sites, such as the Winkler crater in Kansas, that was originally thought to be an impact site, and later discovered to be kimberlite, and a few depressions that were identified in the central Laramie Range and Medicine Bow Mountains. Field examination of many depressions show visible blue ground and carbonate-rich soil, with rounded boulders and cobbles –characteristics that are generally associated with kimberlite. In addition, samples from some sites yield the traditional kimberlitic indicator minerals.

Historically kimberlite pipes were described in 19th century South Africa as having ‘blue ground’, considerable calcium carbonate, and were thought to be old dry stream placers because they contained rounded cobbles and boulders (similar to the cryptovolcanic structures found in the Wyoming craton). The rounded boulders were instead due to country rock fragments that had been rounded and polished in the kimberlite magma as it erupted a few hundred million years ago.

Diamonds from Arkansas - photo
from Glenn Worthington

A few of these structures may represent some of the larger pipes in the world. The best explanation for most of these depressions is that they represent soft, circular deposits of rock that is dramatically different from the more resistant and harder basement granite and gneiss country rock they intrude. Kimberlite typically erupts in circular maar-like volcanoes and is a relatively soft rock. This is why so many kimberlites discovered in Canada as well as in the Wyoming craton form distinct open, treeless parks, with several being submerged under shallow ponds and lakes.

Such structures have been found in the Laramie, Medicine Bow, Front and Seminoe Mountains, the Green River Basin, Bighorn Basin, eastern Kansas, and Alberta. Several hundred were found as far south as Denver Colorado, to as far north as central Alberta, and as far west as Little America to as far east as eastern Kansas. In the vicinity of the Colorado-Wyoming border, Hausel mapped the State Line district with more than 40 diamondiferous kimberlites. Some of these form distinct circular depressions and have already be verified as diamond pipes.

Beautiful, gem-quality diamond with 'trigon' growth platelets on surface - one of many characteristics
of diamond. Photo courtesy of Star Diamond Corporation from their Star-Orion project,
Saskatchewan, Canada.

Unfortunately, only a few of the anomalies and the known kimberlites, lamproites and lamprophyres have been tested for diamond. But nearly all that have been tested yielded some diamonds. The State Line district alone produced more than 130,000 diamonds during testing in past years. No one really knows what awaits discovery here as past diamond testing was inefficient. 

For example, the four diamond mills constructed to test various diamond deposits in the State Line district had many significant flaws & evidence supports that they only recovered a small portion of the diamonds. Even so, gem diamonds >28 carats were recovered along with a octahedral diamond fragment from a larger diamond estimated at 80 to 90 carats. But much larger diamonds were very likely missed by the mills, and these deposits likely contain hundreds of thousands of carats! In Wyoming, kimberlites yielded 50% high-quality gem diamonds. In Colorado, about 30% with gem-quality.

Little effort to outline this resource has been done by the respective state geological surveys in recent years. Research expenditures on diamonds in Wyoming, Colorado, Montana & Kansas has been nearly non-existent compared to the tens of millions of dollars spent for Canadian research along with the hundreds of millions in exploration by companies. Canada now has some commercial diamond mines developed since 1998 an others in the planning stages. In fact, state and federal agencies in the US, which should be conducting research, have only hindered research.

Group of gem diamonds recovered by Cominco America, from Wyoming kimberlites in
State Line district (photo by the author).

Past work has shown that nearly 50% of the diamonds in this craton have been very high quality gemstones. But at the pace that various government agencies are investing to outline this resource (currently non-existent) is shameful and little will happen until a major diamond is accidentally found by a prospector or rock hound.

In Canada, it typically takes $1.5 million per discovery (whether diamondiferous or barren).

KIMBERLITE PIPES

Hundreds of kimberlite pipes occur in a large group of 12 districts within a major diamond province in Colorado and Wyoming. Some of the recently discovered districts enclosed as many as 50 known cryptovolcanic structures (along with potentially dozens of hidden kimberlites). 

Aerial photo showing one of the larger cryptovolcanic structures in North America at Twin Lakes south of Interstate 80 west of Cheyenne. This field includes >50 structures (kimberlites?) outline by distinct vegetation anomalies, depressions in silicate-rich Proterozoic age granites & gneisses in cratonized belt. Most have considerable calcium-carbonate soil (white bull's eyes), 

rounded boulders, are structurally-controlled and located between the State Line and Iron Mountain diamondiferous kimberlite districts.

The Wyoming Geological Survey and DiamonEx Ltd discovered these in the State Line district, the Red Feather Lakes district, the Boulder district, the Happy Jack district, Horse Creek district, Iron Mountain district, Middle Sybille Creek district, Indian Guide district, Harrison district, Twin Mountain district, Eagle Rock district, King Rock district, Strong Creek district, Grant Creek anomaly, Lone Pine field, Lost Lake field, Creedmore Lake field, Chicken Park field, BG field, Lake Owen district, and the Douglas Creek district. Very few of these are tested but provide evidence for one of the largest kimberlite provinces in the world. IN the past, the author mapped the two largest diamondiferous kimberlite districts n Mountain and State Line) in this region.

LAMPROITE AND LAMPROPHYRE

One of the largest lamproite fields in the world (Leucite Hills) and one of the largest lamprophyre fields in North America (Missouri Breaks) occurs in this region, and few of these have been tested even though a group of lamprophyres near Cedar Mountain Wyoming contain diamonds and several lamprophyres have produced diamond-stability minerals, and evidence suggests that one of the largest lamprophyre fields in the world is located in southwestern Wyoming near the Leucite Hills lamproite field.

Estimated erosion level of kimberlite pipes in
the Iron Mountain district (Wyoming) and 
State Line district (Colorado-Wyoming), based
on morphology of pipes and dikes, and kimberlite
 facies. This model suggests about 2,000 to
3,000 feet of the richest parts of the upper
kimberlite pipes were eroded and likely dumped 
hundreds of thousands of diamonds in adjacent
drainages. Yet, only a few drainages were ever
tested for diamond at Fish Creek, George Creek,
and Rabbit Creek, and all three drainages contained
diamond including two diamonds of 5+ carats.

PLACER DIAMONDS

Placer diamonds are likely to be found all over the region, but little exploration has occurred. In the state line district, the kimberlites are deeply eroded providing geological evidence for a very large placer diamond population to occur in the adjacent draininges. To date, only a few samples have been taken in these drainages, yet placer diamonds as large as 6.2 carats were recovered in the past.

 

Airborne input geophysical survey of northern part of State Line diamond district. Several distinct
EM anomalies were detected and suggest possible kimberlite pipes as well as a group of weak
magnetic anomalies of interest.