GemHunter's Guide on How to Identify Raw Diamond

Twin Mountains crypto-volcanic structures south of I-80 between Laramie and Cheyenne.
A few of the many 'kimberlitic' indicator mineral anomalies found by the author that still remain
unexplored. This aerial photo shows a group of circular to elongated ponds surrounded by
 considerable carbonate (white material) that are all  structurally-controlled by faults and sit
within a distinct fold in Precambrian gniess and schist in Wyoming.

Periodically, I receive email, photos, and vials of material from people wanting to know if they have diamonds. Over 30 years, only three out of hundreds of samples actually had raw diamonds. And, although I did not see the stones, I was told diamonds were also recovered from anthills in the Butcherknife Draw area of the Greater Green River Basin in southwestern Wyoming by reliable sources. Another 5 diamonds were reportedly found by a rancher from the Rock Springs-Green River area and, one of my favorite people and good friend, Norma Beers (RIP), found a diamond in an anthill in that same region. 

Nearby, a group of chromian-diopside and pyrope garnet-rich lamprophyre breccias with many fragments of eclogite were initially discovered by a South African diamond mining company years ago, which was followed up by others including Dr. Richard Kuchera an more recently by UP Resources. Everyone who tested these lamprophyre breccia pipes found small micro-diamonds along the southern flank of Cedar Mountain in southwestern Wyoming.

The Boden diamonds. The source of these is still unknown, 

although other diamonds were recovered in 

drill core in this region. Samplers working on a WGS
diamond grant at UW recovered a few dozen samples 

with pyrope garnets nearby (diamond indicator minerals). 

Other anomalies were indentified by prospectors 

working in Douglas Creek and by companies searching 

for diamonds in the 1980s (photo by Jay Roberts)

The first year I worked at the Wyoming Geological Survey in Laramie, a prospector contacted me about two crystals he found in his gold concentrates from Cortez Creek in the Medicine Bow Mountains. So I drove to Saratoga to see the crystals – they were gem-quality diamonds! These were found by Paul Boden and were two beautiful gem diamonds. 

So how does one tell if they have a rough diamond? In my book (Hausel, 2014) I provide information on diamond identification and where these stones have been found in Wyoming. Diamonds have also been found or reported all over the US (Hausel, 1998; Hausel and Sutherland, 2000; Erlich and Hausel, 2002). And after my 2014 book was published, a prospector from North Carolina followed up on a couple of deposits in this book, and in my 1998 book. He found diamonds at a North Carolina occurrence as well as dozens of diamonds including a 5-carat-gem in Rabbit Creek near the Sloan kimberlites in Colorado. These were verified at a university in North Carolina. P.S. if you decide to purchase a copy of my 1998 book, you can find it usually $100 cheaper at the Wyoming Geological Survey in Laramie.

Large group of circular depressions (some filled with water) west of the Iron Mountain kimberlite district in the
Laramie Mountains. These are all structurally controlled and also show evidence of caliche (calcium carbonate) and
lie within the Proterozoic age Laramie Anorthosite Batholith. These still remain unexplored for diamonds! Nearby,
the author also found evidence to two of the largest colored gemstone deposits on earth (still
unexplored!). False color infrared aerial photo over the
Indian Guide crypto-volcanic district. Note the dirt roads for scale.

Sheared Sherman Granite (1.4 Ga) and weathered blue-ground (diamondiferous
kimberlite) (Silurian-Devonian age) exposed in Dozer cut in the Colorado-
Wyoming State Line district (photo by the author).

When it comes to identifying diamonds in the rough, it is important to look at as many characteristics as possible. 

Photos are not a good way to identify a mineral or rock as there are no physical properties one can use. Think about that for a minute - you are sending an image made of pixels - not rock. And nearly every prospector could use a course in photography as 90% of the photos I received in the past, are so poor quality, I'm not even sure if I'm looking at a rock, mineral or the family pet. 

Photos are two-dimensional representations of a 3 dimensional object and retain no physical properties of the specimen - one cannot conduct scratch tests or view inside the minerals to search for mineral inclusions. So it is best prospectors learn to identify diamonds themselves - or visit your state's geological survey - many have a staff member who identifies minerals and rocks for the public. I use to identify hundreds of rocks and minerals for mining companies and prospectors when I was at the Wyoming Geological Survey at the University of Wyoming - back in the old days when the Survey was a functional geological agency and was there to assist companies and the public!

Inducted into the prestigious International Order
of Ragged Ass Miners following a talk in Denver.

At one time, I looked forward to teaching general classes in prospecting for gemstones and gold. There was considerable public interest, just a lack of interest by administrators in various colleges and universities. I was told by one at the University of Wyoming that a class on Geology of Gemstones would be very popular; it was just that it could not be added to their curriculum due to faculty politics! Too much jealousy and interbreeding in the faculty apparently. However, I did teach a few classes in Gold Prospecting and Diamond Prospecting Methods several years earlier through the Extended Studies program at the University of Wyoming, at some prospecting associations and clubs, and for a few geological associations. These were always well attended. I tried to do a similar class at the Gilbert-Chandler and  Mesa Community Colleges in Arizona - same story! 

While at the Wyoming Geological Survey, I lectured to groups on rocks and minerals, which provided me with time to interact with other geologists, general public, rock hounds, mineralogists. Periodically, I learned about various mineral discoveries from the audience. Nearly all were on my own time in evenings, and I received no compensation. The various groups ranged from small rock hound groups to university geoscience departments, to large professional associations all over the country. Some of the more interesting were the RMPTH in Fort Collins, Colorado. This group of treasure hunters invited me to speak to their group at the Allnutt Family Center. Since, I had never been there, I had no background on the group, and when I arrived one evening, I thought someone was pulling a prank - the Allnutt center was actually a funeral home! I almost turned around to head back to Laramie, but decided to at least inquire if there was another place for live people. Sure enough, the treasure hunters were meeting at the funeral home - well, I at least had a captive audience. Years later, I took this group on a field trip to the Chicken Park kimberlites in norther Colorado. They were so overjoyed by the hike to the kimberlites, that they presented me with a special award. Then there was the Society of Economic Geology in Denver, which presented me with their Ragged Ass Miner award! Other groups included the Wyoming House of Representatives, the West Texas Geological Association, Casper Geological Society, Society of Mining Engineers, and one of my all time favorites was the Women's Geological Association in Casper where Martha Horn, president, introduced me by rolling out a scroll across the room from the speakers podium to tell the audience about my accomplishments - that was a wonderful surprise and the first (and I believe only time) I ever received a standing ovation.

Giant, 620-carat diamond photographed at
Wiseman’s Jewelry in Laramie (photo by the author)

Years ago I was invited by Scott Wiseman to stop by his jewelry store in Laramie to examine the largest uncut diamond in the world (at that time). It was being sent around the world for display by a few select jewelers. Imagine this! A 620-carat, priceless giant diamond was sent through First Class US Mail to Laramie, and it was not even insured! This was to be sure  no attention was drawn to the package. Wow! 

I couldn't believe it! I took a couple of photos of this giant - and it is interesting to note that most large diamonds have irregular shapes as seen in the photo. 

In 2008, the diamond market responded to the world economic crisis by taking a nose dive that led to President Bush taking $billions of tax dollars and infusing the money into the economy (we hope) and also passing on bundles of money to Obama. Where did all of this money go? Did anyone think to check their pockets? I'm not saying that politicians can't be trusted - what the heck, is there any politician who can be trusted? Remember that quote by Mark Twain - "Politicians and diapers must be changed often, and for the same reason." Seems like Joe Biden gave a whole new meaning to this quote when he left a deposit with the Pope.

Many diamond companies surrendered to the economic woes in 2008. Many folded around the world, including the company I was consulting for at the time - DiamonEx Ltd. We had a great diamond deposit with a significant diamond resource already identified through previous drilling and trenching that we tied up in Colorado known as the Sloan property. It likely would have been mined by now if it wasn't for the 2008 crash.

Award presented by the Rocky Mountain
Prospectors and Treasure Hunters for one of their
favorite field trips. Award includes a piece of
kimberlite, but the little, rubber chicken didn't
make it.

But some diamond companies survived. Today, much diamond exploration activity is focused on Canada (Hausel, 2007, 2008) and Botswana. And now that Canada is one of the more important diamond sources in the world, one might sit on Santa’s lap and request a diamond from Santa’s workshop at the North Pole. 

Gem diamonds don’t excite me much – it’s their host rocks (kimberlite, lamproite, lamprophyre, eclogite, peridotite) and mineral inclusions I find fascinating. 

About Diamonds 

Diamonds are extraordinary minerals with extreme hardness. Because the genesis of this unique mineral requires extreme temperature and pressure, natural diamond is rare on the earth’s surface. So rare that some diamonds are the most valuable commodity on earth when comparing price to weight. Some high-quality gem diamonds have sold for >$1 million per carat! 

We often hear how valuable gold is – and it is valuable particularly since Congress assumes they were voted in office to spend our money, our children’s money, and our grand-children’s money and great grand-children’s money on theirselves - giving each other raises, buying special healthcare packages, financing sexual harassment accounts for Congress, taking bribes, etc, etc, etc. We have a great country, but something went wrong when the only people who run for office should be sitting behind bars.  Now inflation is starting to jump on the bandwagon and the price of gold is taking off! It seems like it was just in 1971 that gold was selling for $35/ounce. It was! In 1971, the US went off the gold standard. Just recently, gold rose above $1961/ounce: 56 times higher than it was 51 years ago. The Biden crime family (I mean administration) is doing its best to bury the US in runaway inflation.

Some diamonds are incredibly valuable. One sold for >190,000 times an equivalent weight of gold! To me that’s crazy, but rich people have way too much money. Wish they would donate it to my special charity (me) instead. Today, diamonds are mined on several continents. Natural diamond production averages more than 110,000,000 carats annually and is valued at more than $7 billion for raw stones. Most raw stones are not worth much; it is the cut and fashioned stones that bring extraordinary prices. Diamond values dramatically increase after the stones are faceted and the value again increases by dressing them in jewelry, such that diamond jewelry may sell for >10 to 20 times the value of a raw stone – in other words, the original $7 billion equates to >$100 billion in value for a finished product. Not bad for a little crystal made out of carbon (the same stuff you, me, grandma, Fido, fertilizer and Congress are made from). Industrial diamonds, which are considerably lower value, include synthetic industrial diamonds. Synthetic industrial diamond production has an average annual value of around $1 billion per year. 

Former industrial brown diamonds are now worth considerable money. Brown diamonds include Cognac,
Chocolate and other varieties that are now marketed as gemstones (photo by author). 

Due to marketing promotions, some former industrial diamonds are now in great demand  because of labeling. For instance, chocolate, cognac and champagne diamonds used to be considered industrial diamonds because of their color. But now, everyone wants a chocolate diamond. One has to wonder when the industry is going to promote wheat-beer or corn-whiskey diamonds for us red necks. 

Because of extreme value, I suggested to the Wyoming Geological Survey and Wyoming legislature they should consider investing in exploration research and marketing (similar to Canada). Few in Wyoming realize that at least 50% of the kimberlites in Wyoming contain diamonds along with lamprophyre breccia. Of the other kimberlites, lamproites and lamprophyres in Wyoming that supposedly do not have diamonds, only a couple were ever  tested! So we do not know if many of these actually have diamonds or not. 

Another interesting fact: of the diamonds recovered from the Wyoming pipes, at least 50% were gem quality. Just south of Laramie, more than 130,000 diamonds were recovered during exploration, and one commercial mine operated for a short time but closed due to legal problems rather than a lack of diamonds. The mine, Kelsey Lake, can be found on Google Earth along the Colorado-Wyoming border near Highway 287 (40o59’38.55”N;105o30’14.52”W). Then, there are more than 300 crypto-volcanic structures that I identified over the years as well as hundreds of diamond anomalies in Colorado and Wyoming! And this is only the obvious occurrences - most diamond pipes hide along structures and have to be found using airborne magnetic and conductivity (INPUT) surveys.

The Kelsey Lake diamond mine, Colorado, extended north to the Wyoming
border and produced many excellent gem-quality diamonds! (photo by the 
author).

Wyoming, Colorado and Montana could lie within a major diamond province, but we’ll probably never know in our lifetime. It has been reported to take ~ $1.5 million per discovery for a kimberlite pipe (in 2006 US dollars) (whether it contains diamonds or not) in Canada. In Wyoming, my group at the Wyoming Geological Survey  worked with research budgets of $100 to about $10,000/year for diamond projects similar to Colorado State University. The increase in budgets for diamond research was from federal grants and University Grants, not from the legislature. So do the math. 

The reason why diamonds were discovered in Colorado and Wyoming was due to accidents (McCallum and Mabarak, 1976). Diamonds are likely found by a prospector named Frank Yaussi from Fort Collins who operated a gold sluice along Rabbit Creek in Colorado at the location of the Sloan 1 and 2 kimberlite pipes. Frank had no idea that these were diamond pipes at the time, but he recognized diamonds in his placer concentrates - but no one paid attention to an old prospector (Frank Yaussi, personal communication). Anyway, Yaussi recovered some placer diamonds with gold. Later, he started selling some attractive, green, serpentine breccia for terrazzo that was mined on the hillside along Rabbit Creek sometime in the late 1960s or early 1970s. The terrazzo was cut and polished at a plant in Cheyenne Wyoming until the company went out of business after its polishing wheels were scratched beyond repair by the diamonds in the kimberlite! This was an actual outcrop of kimberlite (Sloan 1). It wasn't until 1975, a sample of peridotite recovered from a Wyoming kimberlite was collected by McCallum and Mabarak and sent to the US Geological Survey lab in Denver that diamonds were positively identified. While being prepared for research, the rock was cut and polished and carved several deep scratches in the carborundum polishing wheel. At that point, the rock as dissolved in hydrofluoric acid and several micro diamonds were extracted.

Geological map of the Iron Mountain kimberlite district
by the author

And the only reason that anything was done after the discovery, was because of Dr. Dan Miller Jr., director at the Wyoming Geological Survey at the time –  saw the potential importance, but could not shake much money out of the legislature. But with much less than $1.5 million, about 100 kimberlites were found in Colorado and Wyoming. Imagine how many might be found if these state’s invested just 1/50th of what Canada invests. And this also includes hundreds of kimberlite anomalies we discovered that we never had money to follow up on.

So why should state government invest research funding for diamonds that would one day produce money for a private or public company? This is the concept of research and the concept of how research works on the university level. Universities and certain government agencies are set up to do ground-breaking research. Few companies have money and expertise necessary to do initial grassroots geological research – companies focus on areas that already have been identified to have significant potential for commercial diamonds, and no one is going to pry companies away from Canada when thousands of kimberlites are being found. Canada realized how important the mining industry was to its well-being some time ago, something the US developed amnesia about. Politicians and environmental groups seem to be more interested in importing from China, no matter how toxic the materials, or how much damage is caused to the environment. 

Mines produce a tax base, high paying jobs, research, affiliated industries and more. One of the best swimming facilities in the US was built several years ago in a little town of Gillette, Wyoming. Gillette, one of the driest high deserts in the US produced some of the best swimmers in North America! How could this happen in a town of only 20,000 in the middle of nowhere? Mining! Mining companies built the facility to give back to community of Gillette for the people’s support of their operations. 

Mineralogy 

In nature, native carbon may occur as one of the following polymorphs: diamond, graphite or lonsdaleite (Erlich and Hausel, 2002). The physical differences between these polymorphs are due to the different bonds between carbon atoms. In diamond, the coordination of the carbon atoms is tetrahedral with each atom held to four others by very strong covalent bonds resulting in a mineral that has extreme hardness. 

Frosted cubic raw diamond. Note how greasy this
diamond looks (fact #1)– something that is characteristic of
raw diamond (photo by the author).

In contrast, graphite has six-member hexagonal carbon rings which resonate between single- and double-shared electron bonds which produce sheets of graphite that are strong. However, the hexagonal rings are stacked on top of one another, just like mica and these sheets do not share electrons, only a residual electrical charge. Because of a lack of chemical bonds between sheets, this results in graphite being very soft and having sheets that are easily separated. Now think about this for a few hours - you, me, this diamond and that graphite pencil over there are all made from the same stuff! Carbon! Yet, we all look different. How can that be? Do you still think there is not a guiding intelligence for this universe? 

Then there is an extremely rare hexagonal modification of diamond, known as lonsdaleite. This mineral has a closer-packed arrangement of atoms than diamond or graphite and also shares very strong bonds between atoms resulting in a rare mineral of extreme hardness (Lonsdale, 1971). Lonsdaleite was initially synthesized at temperatures greater than 1,000°C under static pressures exceeding 130 kbar (Bundy and Kasper, 1967). DuPont deNemours and Co. obtained the same transformation by intense shock compression and thermal quenching. Lonsdaleite has since been identified in meteorites and in rare unconventional host rocks: most notable being the Popigay Depression in Siberia (Erlich and Hausel, 2002). The extreme hardness of lonsdaleite makes it ideal for industrial grinding, but its rarity makes it unattractive for commercial use. It is reported to be at least 30% harder than diamond! 

Diamonds are isometric (fact #2) and have high symmetry with common cubic, octahedral, hexoctohedral, dodecahedral, trisoctahedral and related habits. Twinning along the octahedral {111} plane is common in diamond. Often diamonds are flattened parallel to this plane which results in a diamond with flatten, triangular-shaped habit known as a macle. 

Raw diamonds with modified Octahedral crystal habits (photo
by the author).

Cube. Cubes are a relatively uncommon habit for diamond. When found, these are primarily frosted industrial stones. Many diamond cubes have been found in placers in Brazil, and a significant percentage of diamonds mined from the Snap Lake diamond mine in Canada have common cubic habit (Pokhilenko and others, 2003). Crystal faces of a cube often exhibit square-shaped pyramidal depressions rotated 45° diagonally to the edge of the crystal face. The cube may also have scattered trigons mixed with pyramidal and other depressions of hexagonal morphology. 

Octahedron. The octahedron is an eight-sided crystal that has the appearance of two four-sided pyramids attached at a common base. This is a relatively common habit for diamond and seen in just about any diamond parcel (Fact #3). Each pyramid will have four equilateral triangles known as octahedral faces. In nature, these octahedral crystal faces will often have positive or negative trigons (fact #4): small equilateral triangles visible under a 10X hand lens or geologist’s loupe. These are growths or etches on the crystal surface that represent a product of disequilibrium during transport to the earth's surface from the initial stable conditions at depth within the mantle. 

An extraordinary 14.2 carat octahedral diamond
from the Kelsey Lake mine in Colorado
(photo by Howard Coopersmith). 

Partial resorption of the octahedron will result in different crystal habits including a rounded dodecahedron (12-sided) with rhombic faces. Further resorption may result in ridges on the rhombic  faces yielding a 24-sided crystal known as a trishexahedron. 

Many diamonds from Argyle, Australia, Murfreesboro, Arkansas, and the Colorado-Wyoming State Line district exhibit resorbed crystal habits. And 4-sided tetrahedral diamonds are sometimes encountered that are distorted 

octahedrons (Bruton 1979; Orlov 1977). 

Natural diamonds enclose mineral inclusions along cleavage planes. Such inclusions formed in the mantle at about the same time diamond crystallized. These tiny inclusions provide important data on the origin of diamond and may be used to determine the age of the stone or to identify the unique chemistry associated with the genesis of diamond. In a natural diamond, you should be able to see a couple of these with a 10X hand lens unless you found a really good diamond – then you may need a microscope. 

Note the surface of this  slightly yellow diamond. It has several
trigons on the surface (triangular depressions and plateaus)
 seen on most natural diamonds. As a diamond prospector, you
need to become familiar with these and look for them
as well as look at the crystal’s luster – it should look greasy.
Sometimes trigons are in the shape of hexons (6-sided
depressions and sometimes as four-sided depressions,
but trigons are more common) (photo by the author)

Bort. Bort is poor grade diamond used as an industrial abrasive. It forms rounded grains with rough exterior and has a radiating crystal habit. The term is applied to diamonds of inferior quality as well as small diamond fragments. 

Carbonado. Carbonado is a black to grayish, opaque, fine-grained aggregate of microscopic diamond, graphite, and amorphous carbon. The material is hard, occurs mainly as irregular porous concretions and dendritic aggregates of minute octahedra, and sometimes forms regular, globular concretions. Carbonado is characterized by large aggregates (averaging 8 to 12 mm in diameter) that commonly weigh as much as 20 carats. Specimens of several hundred carats are not uncommon. The density for carbonado is less than that for diamond and varies from 3.13 to 3.46 gm/cm3. Because of it having a carbon or burnt appearance, it was named carbonado by Brazilian prospectors. 

Although carbonado had been found in placers in Brazil and Russia, it was not until the 1990s that it was found in situ. Twenty-six grains of carbonado ranging in size from 0.1 to 1 mm were recovered from a 330-lb sample taken from avachite (a specific type of basalt from the Avacha volcano of eastern Kamchatka) (Erlich and Hausel, 2002). 

Physical Properties 

Parcel of fancy color diamonds from Australia
(photo by the author).

Diamond exhibits perfect octahedral cleavage with conchoidal fracture. The mineral is brittle and will easily break with a strike from a hammer. Even so, it is the hardest of all naturally occurring minerals (except for the extremely rare hyperdiamonds). Diamond is assigned a hardness of 10 on the Moh scale and 8000 kg/mm2 on the Knoop scale. 

Corundum (ruby, sapphire), the next hardest naturally occurring mineral has a Moh’s hardness of 9. Thus, diamond will scratch corundum (fact #5). Corundum does not even compare to diamond’s hardness. The Moh’s hardness scale is a little misleading, as it is a 'relative' hardness scale and the difference in hardness between diamond (H=10) and corundum is much larger than that between corundum (H=9) and talc (H=1). A more exact scale is the Knoop scale, which measures mechanical hardness by measuring the pressure applied from a diamond tip. With the Knoop scale, corundum has a hardness of 1370 kg/mm2 which is considerably lower than diamond. Because of diamond’s extreme hardness as well as excellent transparency, diamond is extensively used in jewelry and has a variety of industrial uses. But do not fall for the old adage that whatever scratches glass, is diamond. 

The Argyle diamond mine, Western Australia, as it appeared in 1986
(photo by the author).

Diamond’s hardness varies in different crystallographic directions. This allows for the mineral to be polished with a little less difficulty in specific directions using diamond powder. For example, it is less difficult to grind the octahedral corners off the diamond, whereas grinding parallel to the octahedral face is nearly impossible. 

With perfect cleavage in four directions parallel to the octahedral faces, an octahedron can be fashioned from an irregular diamond by cleaving (Orlov 1977). The specific gravity of diamond (3.516 to 3.525) is high enough that it will concentrate in placers with “black sand”. So for those gold panners who are reading this, watch for diamonds! A few hundred diamonds were recovered with gold in California during the gold rush in the 1800s. And it is very likely that thousands of diamonds were discarded by the gold prospectors. Diamond’s density is surprisingly high given the fact that it is composed only of carbon – a light atom. But compared to graphite, diamond is twice as dense due to the close packing of atoms. 

Absolutely beautiful diamonds (photo courtesy and
copyright by of Rio Tinto

Color. Diamonds occur in a variety of colors including white to colorless and in shades of yellow, red, pink, orange, green, blue, brown, gray and black. Those that are colored are termed fancies. Colored diamonds have included some spectacular stones – at a 1989 Christie's auction in New York, a 3.14-carat Argyle pink diamond sold for $1.5 million. A 0.95-carat fancy purplish-red Argyle diamond sold for nearly $1 million (US). More recently, the highest price in history was for a pink diamond that originated from the ancient Golconda mines of India. The Golconda diamonds are thought to have come from olivine lamproite similar to the rock type at Argyle, Australia. This pink diamond was sold at a Sotheby’s auction for US$46 million for the 24.78 carat diamond ($1.86 million/carat). The world’s largest faceted diamond, a yellow-brown fancy known as the 545.7-carat Golden Jubilee (Harlow, 1998), is considered priceless. Possibly the most famous diamond in the world, the 45-carat Hope, is a blue fancy. 

In most other gemstones, color is the result of transition element impurities; however, this is not the case for diamond. Color in many diamonds is related to nitrogen and boron impurities or a result of structural defects. Diamonds with dispersed nitrogen may produce yellow (canary) gems. If the diamond contains some boron it may be blue, such as the Hope diamond. The Hope was found in India; however, many natural blue diamonds have also come from the Premier mine in South Africa. Blue diamonds with traces of boron are referred to as type IIb, and are semiconductors. Natural irradiation may also result in blue coloration in some diamonds (Harlow, 1998). 

The most common color for diamond is brown. Prior to the development of the Argyle mine in Australia in 1986, brown diamonds were considered industrial stones. But due to Australian marketing, brown diamonds are now highly prized gems. The lighter brown stones are labeled champagne and the darker brown referred to as cognac. Yellow is the second most common color and such stones are referred to as “Cape” diamonds in reference to the Cape Province of South Africa. When the yellow color is intense, the stone is referred to as “canary”. 

Pink, red and purple diamonds are rare. The color in these is concentrated in tiny lamellae (referred to as pink graining) in an otherwise colorless diamond. The color lamellae are thought to be the result of deformation of the diamond structure. 

A green modified octahedral diamond from
undisclosed location (photo by the author)

Green diamonds are different. Even though there are many green diamonds, few are faceted, primarily because most have a thin green surface covering clear diamond such that if the stone is faceted, the green layer is removed. Faceted green diamonds are so rare that only one is relatively well known (the 41-carat Dresden Green) that is thought to have originated in India or Brazil. The color in most green diamonds is the result of natural irradiation. Other green diamonds may result from hydrogen impurities. Another variety, known as a green transmitter produces strong fluorescence that tends to mask the yellow color of the stone. Other colors include rare orange and violet diamonds (Harlow, 1998). 

One of the better-known black diamonds is the 67.5-carat Orlov. Black diamonds are colored by numerous graphite inclusions, which also make the diamond an electrical conductor. These are difficult to polish due to abundant soft graphite, thus black gem diamonds are uncommon. Opalescent, or fancy milky white diamond, is the result of numerous mineral inclusions and possibly nitrogen defects in the crystal (Harlow, 1998). 

Dispersion, transparency, conductivity, wet-ability. Diamond has high coefficient of dispersion (0.044): the coefficient being the difference in refractive index of two visible light wavelengths at the opposite ends of the spectrum (one blue-violet and the other red). This produces the distinct fire seen in faceted diamond. Diamond is completely transparent to a broad segment of the electromagnetic spectrum making it useful in a variety of industrial, electrical and scientific applications. It is also transparent to radio and microwaves. Colorless diamonds are transparent to visible light wavelengths extending into the ultraviolet, and a few rare diamonds (Type II) are transparent over much of the ultraviolet spectrum. 

Diamond has a luster described as greasy to adamantine that is related to its high refractive index (IR=2.4195) and density. Such high density greatly diminishes the speed of light. For example, the speed of light in a vacuum is 186,000 mi/sec, but in diamond, it is only 77,000 mi/sec (Harlow, 1998). 

Resorbed diamond crystal habits - Argyle diamonds Australia.
Photo by the Author.

Many diamonds are luminescent: approximately one-third luminance blue when placed in ultraviolet light. In most cases, luminescence will stop when the ultraviolet light is turned off (known as fluorescence). Diamonds fluoresce in both long- and short-wave ultraviolet light. The fluorescence is usually greater in long wave and diamond may appear blue, green, yellow or occasionally red. However, fluorescence is weak, and it may not be readily apparent to the naked eye. In some cases, light emission is still visible for a brief second after the ultraviolet light source is turned off (known as phosphorescence). Some diamonds may also show brilliant phosphorescence when rubbed or exposed to the electric charge in a vacuum tube; or when exposed to ultraviolet light (Dana and Ford, 1951). 

At room temperature, diamond is four times as thermally conductive as copper (fact #6), even though it is not electrically conductive. Because of the ability to conduct heat, diamond has a tendency to feel cool to the lips when touched, because the gemstone conducts heat away from the lips. This is why diamonds have been referred to as “ice”. 

GEM (also referred to as Diamond Detectors, Diamond Detectives) testers (about the size of a pen) are designed to identify the unique thermal conductivity of diamond and distinguish it from other gems and imitations. This one tool can be very useful to a prospector due to the fact that it sells for a reasonable price – and if you think you have raw diamonds, get one of these. 

Grease table. We used a 10:1 mixture of Vaseline
to paraffin to extract diamonds from concentrates
(photo by the author). 

Diamonds are hydrophobic (non-wetable) (Fact #7). Even though diamond is 3.5 times heavier than water, it can be induced to float on water. Because it is hydrophobic, diamond will attract grease, thus providing an efficient method for extracting diamond from ore concentrates (i.e., grease table). Oil, grease, and other hydrocarbons have an affinity for materials that do not contain oxygen (such as diamond). 

Diamonds are unaffected by heat except at high temperatures. When heated in oxygen, diamond will burn to CO2. Without oxygen, diamond will transform to graphite at much higher temperatures (1900°C). Several years ago, I tried to burn a diamond using a Bunsen burner with added oxygen, and burned a diamond to graphite plus plant food (CO2). Diamonds are unaffected by acids. 

REFERENCES CITED 

• Bruton, E. 1979. Diamonds. Radnor, Pennsylvania: Chilton Book Company. 532 p. 
• Bundy F.P., and J.S. Kasper, 1967, Hexagonal diamond, a new form of carbon: Journal of Chemical Physics. v. 46, no. 9, p. 3437–3446. 
• Dana, E.S. and Ford, W.E., 1951, A textbook of Mineralogy (7th Edition): John Wiley & Sons, New York, 851 p. 
• Erlich, E.I., and Hausel, W.D., 2002, Diamond Deposits – Origin, Exploration, and History of Discoveries: Society of Mining Engineers, 374 p. 
• Harlow, G.E., 1998, The Nature of Diamonds: Cambridge University Press, 278 p. 
• Hausel, W.D., 1998, Diamonds and mantle source rocks in the Wyoming Craton, with a discussion of other US occurrences: Wyoming State Geological Survey Report of Investigations 53, 93 p. 
• Hausel, W.D., 2007, Diamond deposits of the North American Craton: Colorado Geological Survey Industrial Minerals Forum, 48 p.  
• Hausel, W.D., 2008, Diamond Deposits of the North American Craton in Woods, A., and Lawlor, J., eds, Topics in Wyoming Geology, Wyoming Geological Association Guidebook. p. 103-138. 
• Hausel, W.D., 2009, Gems, Minerals and Rocks of Wyoming. A Guide for Rock Hounds, Prospectors & Collectors. Booksurge, 175.
• Hausel, W.D., 2014, A Guide to Finding Gemstones, Gold, Minerals and Rocks: GemHunter publications on Amazon, 368 p.
• Hausel, W.D., and Sutherland, W.M., 2000, Gemstones & Other Unique Minerals & Rocks of Wyoming - A Field Guide for Collectors: Wyoming Geological Survey Bulletin 71, 268 p. 
• Lonsdale, K. 1971. Formation of lonsdaleite from single-crystal graphite. American Mineralogist 56:333-336. 
• McCallum, M.E., and Mabarak, C.D, 1976., Diamond in State Line kimberlite diatremes, Albany County, Wyoming and Larimer County, Colorado: Geological Survey of Wyoming Report of Investigations 12, 36 p. 
• Orlov, Yu.L. 1977. The Mineralogy of Diamond. New York: John Wiley. 233 p. 
• Pokhilenko, N.P., Zedgenizov, D.A., Afanasiev, N.P, Rylov, G.M., Milledge, H.J., Jones, A. Hall, A.E., and Reimers, L.F., 2003, Morphology and internal structure of diamonds from the Snap Lake/King Lake kimberlite dyke system, Slave Craton, Canada: 8th International Kimberlite Conference Program w/Abstracts, Victoria, B.C., p. 90-91. 

Diamonds, kimberlites, lamproites and related anomalies in the Colorado-Wyoming province (source - W. Dan Hausel,
1995).

MOST VALUABLE GEM 

Nov. 2010: A rare pink diamond sold for the highest price in history at an auction in Switzerland. The 24.78 fancy pink diamond was sold at a Sotheby's auction for a record US$46 million (or $1.86 million/ct). This beat the old record for the 35.56-carat Wittelsbach blue diamond that sold for more than $24 million in 2008. The emerald cut pink diamond was apparently last seen on the market 60 years ago. Another diamond that is up for auction is also expected to bring a high price - a pear-shaped 26.17 carat flawless diamond from the ancient Golconda mines of India. - (European Press Association).