Diamond indicators at the Crater
By Waymon Cox
Greetings from Crater of Diamonds! A common question asked by many first-time park visitors is “Where’s the best place to look for diamonds?” Generally, we advise people to look anywhere in our plowed 37.5-acre field, as it includes the type of soil known to contain diamonds. But if you know about the “associates” of a diamond, you can narrow the search down a little more!
Certain minerals found at Crater of Diamonds State Park are known as “indicators” of diamonds. These minerals are helpful for geologists studying volcanic pipes around the world, and they are also useful for Crater visitors wanting to know whether they are digging in a good location.
Generally speaking, diamonds may be found anywhere in our search area, buried under the volcanic soil. However, as we’ve experienced time and again this summer, rainfall has a big effect on the search area through erosion. Diamonds are heavy for their size. Often they may be uncovered and left for some lucky visitor to find, while others are moved as rain washes through the field. These are then deposited in trenches and other low areas, along with other heavy stones including diamond indicators.
When digging in these low spots for diamonds, it is best to use a screen set
and water to separate the gravel by size, then by weight, settling the “heavies” in the bottom-center of the screen.
After the sifted material is dumped out of the screen, an accumulation of small, dense rocks and minerals can be found at the top-center of the pile.
Rocks and minerals are concentrated by weight when wet sifting.
When the material is thrown on a flat surface, diamonds and other heavy materials appear on top, near the center of the pile.
For many miners, the prospect of searching through this concentration for a diamond seems tremendous. But by looking closely, shiny, colorful treasures may be found which point the way to diamonds. Chromite spinel, chrome diopside, and pyrope garnet are all great indicators to look for!
Chromite spinel is the most common indicator mineral to find when wet sifting. Chromite is a black, opaque crystal with shiny irregular facets that formed in Earth’s mantle. Occasionally it may be found in an octahedral shape. Like other indicator minerals, chromite is fairly dense, with a specific gravity of about 4.5.
Chrome diopside is not as common as chromite, but it is easier to see. Chrome diopside is a diopside gemstone, with a characteristic lime green color. Like chromite, it is also found in very tiny pieces at the Crater. With a specific gravity between 3.25 and 3.55, it is closest to the diamond’s specific gravity of 3.52.
One of the best-known indicator minerals for diamonds is pyrope garnet. Pyrope is the only member of the garnet family to display a rich, red color in natural samples. Formed under similar conditions as diamonds, pyrope is often used by geologists when pinpointing the locations of hard-to-find lamproite and kimberlite volcanic pipes. Pyrope garnets have a specific gravity of 3.78 and are – once again – very small crystals at the Crater, transparent in appearance, with a reddish-purple color.
Minerals such as chromite spinel (black), chrome diopside (green), and pyrope garnet (red) have similar specific gravities to diamond.
All three of these serve as very good indicators for diamonds but should not be taken as a guarantee of a diamond find
Instead, they should be seen as what they really are – beautiful and unique tiny treasures from Crater of Diamonds State Park!
Search area last plowed: August 26, 2009
Diamond finds for September 7 - 8, 2009:
September 7 – Sharrol Frederick, Sherwood, AR, 9 pt. white; Denis Tyrrell, Murfreesboro, AR, 40 pt. yellow; Glenn Worthington, Springdale, AR, 4 pt. white
September 8 – Ryan Retzloff, Indianapolis, IN, 19 pt. white
(No diamonds have been found since September 8.)