Crater of Diamonds Newsletter

You might wonder how the staff can tell whether or not the little rocks that our visitors bring up to the rock identification desk are actually Crater diamonds. This is a good question, and sometimes it is not as easy as just looking at it. However, when we look at our visitor’s rocks most of the staff members have seen hundreds of diamonds.

So, we look for several characteristics. First, does the rock have an almost unnatural shine? That shine of cut diamonds is not created solely in the cutting process, it is only enhanced. Our rough or natural Crater diamonds almost always have a shiny surface that is unlike any other rock or mineral that can be found out on our field. Second, we look for facets or crystal faces on the surface of the rock. Our diamonds are different from African diamonds, because they generally have 24-sides, or, when they are perfect and unbroken, they are tetrahexahedrons. Even the most broken, or misshapen Crater diamonds generally have at least some of those crystal faces still showing on their surfaces. Third, the 24-sided shape gives them a rounded appearance. Most of the quartz crystals that our visitors bring up have sharp edges, or come to a point. Quartz crystals also often have little orange to yellow-orange colored areas. Those areas are the result of iron staining. Some of the Crater diamonds are yellow, but that color is from nitrogen, not iron, being caught in the crystal structure as the diamond crystallized. The yellow diamond color is a true yellow, with no orange—which is the reason that yellow diamonds are called canary diamonds. Finally, only a few diamonds have a frosted outside that keeps the observer from being able to see into their insides. If the little rounded rock that our visitor brings up is opaque, it is usually a rounded piece of jasper. However, unlike glass, diamonds are not transparent, so generally we can’t see all the way through them. The characteristic of diamonds that creates the shine also makes it difficult to see through them.

Even after checking for all of these characteristics, sometimes the rock is too small to see the crystal facets or some of the other characteristics. So, we take them into our office and look at them with our powerful binocular microscope. Even after looking through that microscope, especially if the stone has one of the diamond characteristics, but no others, we still may be sitting on a fence about whether or not the rock is a diamond. At that point we are usually trying to decide whether the stone is a well rounded and faceted quartz crystal or it is a diamond.

So, we have two more tests that we can use. We have a Presidium gem tester, which uses an electric probe to test the thermal conductivity of the rock. Diamonds are good thermal conductors. The probe has two parts. One heats the stone and the other measures the amount of heat that the rock contains after heating. The test takes 2-3 seconds and the meter has a readout from glass to diamond. However, this test can give a false positive if you are holding the stone in your fingers. Therefore, we have a final, fairly definitive test. For this test we use a fluid called methylene iodide. The thickness or viscosity of the fluid is such that quartz crystals will float on the top of the fluid and diamonds will sink to the bottom. We save this test for the truly puzzling stones, because the fluid has to be handled very carefully. It is corrosive and can cause burns, and it is also cumulatively carcinogenic. Therefore, it is harmful if inhaled or absorbed through the skin. So, dropping the possible diamond into this fluid is a last resort.

Finally, if it passes the fluid test, but does not register as a diamond on the thermal test, we send the visitor to Mike Howard, a mineralogist who works for the Arkansas Geological Survey. He has been looking at Crater diamonds for 30 years, and is the final arbiter of any questionable diamonds.

Search area last plowed: October 10, 2011; Most recent heavy rain: September 18, 2011

October 3 - Brenda Judkins, Carrollton, TX, 47 pt. white; Dan Zenor, Quitman, TX, 12 pt. white

October 4 - Connie and Rusty Gray, Lesage, WV, 10 pt. white, 23 pt. white, 41 pt. white

October 6 - Bill Hines, Milton, FL, 2 pt. white, 3 pt. brown, 5 pt. white, 5 pt. brown, 7 pt. white, 7 pt. white, 8 pt. yellow, 11 pt. white, 13 pt. white, 19 pt. white, 19 pt. white, 25 pt. yellow, 32 pt. brown,

October 8 - Carole Leger, Owassa, OK, 81 pt. white; Tim Pittman, Jacksonville, AR, 3 pt. white, 7 pt. brown