GREEN RIVER - What do the solid green ant hills in the Leucite Hills northeast of Rock Springs have that other ant hills in Wyoming don't have?
Thousands of carats of gem-quality peridot, for one thing.
Several years worth of research by the Metals and Precious Stones Section of the Wyoming State Geological Survey (WSGS) has recently identified a handful of gemstones like peridot that were not formerly known to be in Wyoming.
Not only does Wyoming have 23 known diamond deposits, it also has a number of colored gemstones including sapphires, iolites, garnets and chromian diopside that have been identified by geologists in the past few years.
Geologists continue to add more to the list, WSGS Senior Economic Geologist W. Dan Hausel said in an interview Tuesday.
"It's amazing what we don't know about (gemstones) in this state," Hausel said. "We're still finding new gemstones all the time."
Hausel said a recent diamond hunt in the Leucite Hills area of the Red Desert in southwest Wyoming turned up an interesting deposit of the colored gemstone peridot, a quality gem found in olivine deposits.
Peridot usually occurs in rocks intergrown with other materials. The island of Zabargad in the Red Sea is one of the few places in the world where peridot crystals with very distinct facets is found.
Olivine was first reported in the hills in the 1960s, but researchers paid little attention to the quality of the olivine until the WSGS examined it, Hausel said.
"I was out there doing some work looking for the possibility of diamonds and one of the indicator minerals we look for is olivine, which is kind of greenish," he said.
"I was out sampling when I came across a couple of ant hills that were solid green with olivine," Hausel said.
"I took two ant hills back and we processed them and we got 13,000 carats of olivine and most of it contained gem-quality material," he said. "We had some of it cut recently and it produced some very nice peridot. It's a very attractive gemstone."
He said it took about 3 million years to form the Leucite Hills, which contains extremely rare volcanic rocks. "Olivine if formed in a matter of minutes or hours (in cooling lava) … it's a very rare event."
Hausel said ongoing research on mineral deposits discovered by the WSGS in 1995 in the Palmer Canyon west of Wheatland has also revealed the presence of other gemstones such as corundum, which produces attractive pink to red sapphires.
Corundum is next to diamonds in hardness, so gemstones like sapphires are resistant to wear. Australia is the largest producer of blue and golden sapphires. Other producers include Thailand and several countries in East Africa.
The Palmer Canyon deposit also contains transparent, blue cordierite (known as iolite), which is a popular sapphire-blue gemstone. Hausel found specimens of gem-quality iolite that weighed more than 3,000 carats and were about fist-sized.
"We didn't cut those because they are much more unique as a geologic specimen," he said.
He said based on the similarities in geology, the WSGS also believes that similar deposits of those gemstones may be discovered at several other locations across Wyoming.
Other gemstones found recently include purple to yellow-orange pyrope garnet, which was popular in the 19th century, and emerald-green chromian diopside. Both finds have yielded gemstones with very rich colors at a number of locations in southern Wyoming. The gemstones are sometimes found in diamond deposits.
More information on gemstones in the state can be found at the WSGS website ( http://www.wsgsweb.uwyo.edu/metals/ ).
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