How to Recognize Rough Diamond

Beautiful, flawless diamonds in the rough
from the Argyle Mine in Australia.
Photo "Copyright © 2014 Rio Tinto.".

After my book on Finding Gemstones was published, I heard back from several prospectors and rock hounds who used it, to find many gemstones in Wyoming that include gem pyrope garnet, chromian diopside, agate, opal, labradorite, ruby and even diamonds. One prospector reported he had found a large cache of diamonds including a flawless, 6-carat, diamond, just by panning near the Sloan kimberlites in Colorado! This was not surprising at all, because the Sloan kimberlites produced hundreds of diamonds during testing of the property by three different companies, and prior to that, a Fort Collins prospector - Frank Yaussai, use to extract diamonds and gold from Rabbit Creek adjacent to the kimberlites. And, when I was the VP of US Exploration for DiamonEx Ltd, we had plans to develop these kimberlites into a small mine, but the 2008 economic crisis put the company out of business just as they were making some headway. So, these kimberlites and the adjacent Rabbit Creek and alluvial gravels, are rich in diamonds!

Not long after my gemstone book was published, I was contacted by a prospector who found some diamonds in North Carolina based on this and another book I wrote in 1998 on diamonds in the US. So, get a copy and get out looking for some gemstones!

Others found several precious opals and some fire opal and another reported a new sapphire deposit. Others sent letters, email, and photos of the spectrolites and moonstones found because of my book - and these are just a few of the people who are out there prospecting and using my book. So, get a copy, and get out there and look for some gemstones - there are many, many deposits in Wyoming and nearby. Even some giant iolite gem deposits that remain mostly unexplored.

Diamonds are hard. They are considered the hardest natural mineral, although there are some extremely rare forms of carbon that are even harder. Even so, diamond will scratch your windshield. When geologists discuss mineral hardness, one simple scale which is often mention is that of Moh's scale. This is a relative hardness scale and specific minerals have been assigned relative hardness from 1 to 10. Diamond tops the scale at 10. 

In my new book entitled, 'A Guide to Finding Gemstones, Gold, Minerals and Rocks', I discuss the hardness of diamond as well as problems that prospectors have in identifying diamonds. Many have the impression that what ever scratches glass, is diamond. Well, this is only partly true. 

Diamonds are isometric (equal-dimensional)
and typically have crystal habits of a
octahedron or some modified version.

Have you ever replaced your windshield in the windy states of Arizona or Wyoming because your windshield became so pitted by blowing dust that the glare off the pits was making it difficult to see? Now think about this, has your windshield been bombarded by thousands of tiny diamonds?  

It turns out that a windshield on a car (or a prospector's truck) has a Moh's hardness of only 5.5 to 6.0. It's true that diamond is harder and will scratch your window, but so will corundum, topaz, quartz, most feldspars and many other silicates like amphibole and pyroxene. So, please do not scratch your windshield as a test. Instead, learn the physical properties of this mineral, or use something that eliminates the problem - something that jewelers use all the time - a 'Diamond Detector'. You can find these on eBay for very reasonable prices.

When I was at the University of Wyoming, periodically, people would call to ask about diamonds they found. One prospector called me from Jeffrey City, Wyoming to ask about the hundreds of diamonds he was finding nearby.

"Diamonds, diamonds, diamonds - I'm finding them everywhere I look"! 

Being suspicious, since I've heard so many similar claims, I asked the prospector how he was identifying them?  

His response - "I just scratch the windshield of my truck"

I responded, "Are you going to be able to see when you drive home?"

On the other end of the phone there was silence as he contemplated my comment - guess it wasn't what he expected. And after I explained to him about the hardness of diamond along with quartz and other silicates - all being harder than window glass, he hung up.

Some of the common indicator minerals associated with
diamond include pyrope garnet, chromian diopside, olivine
and a few other minerals. Note all of these that I collected in
Wyoming are gem-quality.

But as far as the host rocks and the beautiful 'diamond indicator minerals' associated with many diamonds, you will need to study their physical properties and characteristics to be able to recognize them. To assist in this endeavor, I put together some websites - one specifically on diamonds.

Exodus 28:18