By John J. Bradshaw, G.G.
Some gems had already formed when Pangea was the single continent 300 million years ago, and many more have formed since that time. Geological processes are extremely slow, but because of the immense lengths of time involved, huge physical changes have occurred and will continue to occur, possibly resulting in more gemstone discoveries through erosion and mining.
Think about it: Mountains are created and destroyed; oceans swallow up land and then recede; continents form, break up, and move over the surface of the Earth; coastlines change; and rivers and glaciers erode huge valleys. When these shifts occur, gemstones are created, discovered, collected, and treasured by rockhounds.
Popular gemstones are found throughout the world, and the United States is home to quite a few! From Diamonds to Amethyst, Tourmaline, Peridot, Opal, and more, gem nerds have plenty of places to look. Read on to see what you can find and where.
Amethyst was found in Sweden, Maine, at the Saltman Prospect during a road installation in 1998. The material, however, was completely mined out in a year and a half.
Ongoing mining of the purple gem currently takes place at the Four Peaks Mine in the Mazatzal Mountains northeast of Phoenix, Arizona. This site was discovered in the early 1900s by a prospector looking for gold. Four Peaks is one of the few (perhaps the only) U.S. mines requiring supplies to be brought in, and Amethyst is removed twice a year by helicopter.
Miners stay on-site for upwards of two weeks after a nine-mile hike to the site, where there is no running water or electricity. All the mining is done by hand.
Solar-powered batteries are used to light and ventilate the mine. Yield is approximately 1,000 carats of finished gems for 1,000 pounds of mine run. The rough is often heavily zoned, further reducing yield.
Amethyst is also found in Jackson’s Crossroads, Wilkes County, Georgia. The gemstone was discovered in 1988, with high-end mineral specimens first offered at the Tucson gem shows in 2005.
Aquamarine is the state gemstone of Colorado, found on Mt. Antero in Chaffee County. Aquamarine crystals are found in vugs in pegmatite, mostly at the 12,000-foot level. The mining season is limited to just a few months due to weather conditions, and Colorado Aquamarine is light-medium to medium in tone with good clarity.
The Morenci Mine in Morenci, Greenlee County, Arizona, is a source of fine specimens and rough Azurite and Malachite. It’s not often used in jewelry due to its low hardness of 3.5–4, but material set into pendants and earrings is typically fine.
Benitoite was found in a single source in San Benito County, California. The gemstone was discovered in 1907, and the mine is now permanently closed, though collectors and dealers still clamor for it. Benitoite is largely blue and is often color zoned. Available gems are mostly in small sizes (less than a carat in weight). In my experience, it is the No. 1 rare gemstone asked for and sold in Tucson! All my Benitoite in Tucson is sold through my other company, Coast to Coast Rare Stones.
Only two Diamond mines in the U.S. produced thousands of carats of rough. Colorado’s Kelsey Lake Mine was operational from 1996–2001, and the Crater of Diamonds State Park in Arkansas has been a steady but modest source of Diamonds since the mid-1800s. The first Diamond was found in 1906 by a local farmer, and more than 33,000 Diamonds have been found since it became a state park in 1972. Visitors get to keep what they find. The most common colors of Diamonds found are white, brown, and yellow, and .25 ct. is the average size. Notable rough Diamonds found include the 40.23 ct. “Uncle Sam,” the 18 ct. “Canary Diamond,” the 16.37 ct. “Amarillo Starlight,” and the 15.33 ct. “Star of Arkansas.”
The only significant Emerald deposits in North America are in Alexander County, Mitchell County, and Cleveland County, in North Carolina. However, even that material is not available in commercial quantities. The top 20 largest crystals found range from 433 to 1,869 carats, and six of the top 20 were found in 1971. Many are in museums now.
Fluorite has been found at the William Wise Mine in Westmoreland, N.H, a site that was actively mined for specimens and rough in the late 1980s through the 1990s. Fluorite is rarely used in jewelry due to lack of durability—it’s soft with a hardness of four and four directions of cleavage! Colors range from green to purple to yellow.
Fluorite, including deep blue colors, is also found in Illinois. The largest Fluorite in the world is a deep blue from Illinois, weighing 3,965 cts. It was cut by my company in late 1987 and resides in the Smithsonian.
Spessartite-variety Garnet is found in California and Virginia, while Almandine Pyrope is in Massachusetts and Arizona.
The spessartite Garnet found at the “Little 3 Mine” in Ramona, California, was discovered in 1903. Upwards of 40,000–50,000 carats of facet-grade rough were produced between 1956 and 1994. Before the African spessartite finds of the late 1990s, California was an important source. However, the mine has been closed for a couple of decades with no plans to reopen.
Spessartite Garnet was also found in Rutherford Mines in Amelia Court House, Virginia, which was primarily mined for gem Amazonite between 1912 and 1932. To date at that location, over 50 mineral species have been found, and the mines were active up until 1959, with the occasional prospecting of the dump tailings since.
Chrome Pyrope Garnet is found on the Navajo Reservation in Arizona and is nicknamed “Ant Hill” Garnet because the crystals are excavated by ants while digging their burrows. These Arizona Garnets are actively mined and are almost always less than 1 carat in weight with an intense deep red color.
Almandine Garnet is found at the Red Embers Mine—previously named the Two Fat Guys Mine—in Irving, Massachusetts. Dark red Garnets are found in a graphite matrix, cut stones are small, and larger gems are dark in color. That mine has been active since the early 2000s.
This graphic hard stone shares the honor of being the state’s gemstone with Sapphire. Montana Agate is found in the alluvial gravels of the Yellowstone River. The unique patterns in these Agates are available in a wide range of shapes and is characterized by red iron oxide and black manganese oxide.
In Montana, there is hard rock mining in Yogo Gulch, alluvial deposits in El Dorado Bar, and eluvial deposits at Rock Creek.
The Yogo Gulch Mine was reopened by Yogold USA Corp. in 2022. Yogo rough tends to be small and mostly flat crystals which limits larger cut stones with proper proportions. Colors are both blue and purple with no need for heat treatment. Most faceted Yogos are less than .50 carat in weight.
El Dorado Bar is one of the largest and most actively mined operations on the Upper Missouri River. Gems were discovered there in 1865, the earliest in the state, and its Sapphire deposits are found in gravel bars along the riverbank. Overall, these Sapphires are larger than those found in other Sapphire mines in Montana. Greenish-blue and bluish-green colors are the most common to find but do not react well to heat treatment. The site is open to anyone who pays a fee to the mine owners to dig.
The Rock Creek Sapphire Mine has been operated by Potentate Mining since 2011. (Look for a feature article on it in Prism Volume III, out soon!) Five acres are mined at a time and reclaimed before moving on. Mining takes place from late spring through the fall, weather permitting, and the material responds well to heat treatment, producing a wide range of colors.
Faceted stones are mostly sub-carat, and only 2%–3% are 1 carat or larger.
This pink gem has been found in Buckfield, Maine, and at the Stewart Mine in Southern California, also known for its Tourmaline.
This apple green, sage, and black gem was first found in Wyoming in the 1930s. Nephrite is gemologically different from Jadeite and doesn’t match the best green of Jadeite. China is the principal market for both Jadeite and Nephrite. Nephrite belongs to Actinolite/Tremolite series, with lighter colors closer to Tremolite and darker colors possessing more iron and thus closer to the appearance of Actinolite. Nephrite Jade can also be found in Washington.
Opal is found in Virgin Valley, Humboldt County, Nevada, in silica-rich water in buried tree limbs, effectively opalizing original tree parts. It’s rarely used in jewelry due to heavy crazing. Fire Opal is also found in Oregon, and pale blue Opal with flash is found in one mine site in Arizona.
This love-it-or-hate-it lime green gem is found on the San Carlos Apache tribal lands in Arizona and is one of the richest and largest sources of Peridot in the world. The gemstone is mined mostly with hand tools by tribal members from the basalt known as Peridot Mesa. Most cut stones are less than 3 carats in weight, with the largest to date weighing 34.65 carats.
Gem-quality red Beryl is only found in one location, the Ruby-Violet Claims in the Wah Wah Mountains in Beaver County, Utah. That mine is now closed, though collectors can still find old material in the market.
The gem was originally called Bixbite after Utah miner Maynard Bixby, but the name was changed to red Beryl to remove confusion; the mineral Bixbyite is named for the same person. Red Beryl is exceptionally rare to find, with the Utah Geological Survey estimating that one crystal of red Beryl is found for every 150,000 gem-quality Diamonds. Faceted stones typically weigh less than 1 carat, although larger stones exist. The gem is rarely eye clean and is typically fracture filled with oil or resin products.
Tiny crystals of red Beryl have also been found in Wildhorse Springs, Topaz Valley, and Starvation Canyon, all in Utah, as well as in New Mexico and Mexico, but they are too small or imperfect to facet. Red Beryl is also sometimes incorrectly called red Emerald.
Rhodochrosite was mined at the Sweet Home, now closed, and at the Detroit City Mine on Mount Bross in Alma, Colorado. The Sweet Home was founded as a silver mine in 1872, where miners collected, traded, and sold Rhodochrosite as a by-product. Some high-end mineral specimens and cutting rough are still found today. Fun fact: Rhodochrosite is magnetic.
The Jacobs Ruby Mine in Cowee Valley, Macon County, N.C., has turned up facet-quality gems of less than 3 carats, while gems from the Rock Creek Mine near Philipsburg, Montana, are rare to find and largely less than .75 carats in size.
Spodumene – Kunzite
Kunzite was first discovered in 1902 in San Diego County, California. The gem was named after George Frederick Kunz who confirmed this was a new color of Spodumene. The Oceanview Mine in Pala, San Diego County, is currently active for Kunzite—pink to purple-pink colors—and other minerals. The color is caused by manganese.
Spodumene – Hiddenite
Hiddenite was first found in Hiddenite, Alexander County, North Carolina, in 1879. The gemstone and the town are both named after William Earl Hidden, sent to the state by Thomas Edison to find platinum. The gem is colored by chromium, ranges in color from yellow-green to bright chrome green, and is usually found in weights of less than 5 carats.
This is the state gem of Oregon (since 1987), the only place in the U.S. where it’s found. There are three major mines in southeast Oregon—the Ponderosa Mine, the Sunstone Butte Mine, and the Dust Devil Mine. This Oregon material is Labradorite, a variety of plagioclase feldspar, which is the among the world’s most common minerals. But the Oregon variety is copper bearing and found nowhere else in the world.
The Pikes Peak area in Colorado—there are several localities within 1,000 square miles—was first discovered in 1880 as a source of Topaz. Colors are colorless to sherry-orange, which can fade to colorless in daylight.
Tourmaline was mined in San Diego County, California, at the beginning of the late 1800s. The gem’s biggest fan was Tzu Hsi, the Dowager Empress of China, who loved pink Tourmaline and ruled China until her death in 1911.
Between 1902 and 1910, tons of gem-grade Tourmaline were mined, with most going to the Empress. California material was available in a variety of colors, with pink and green the most common. Blue Cap Tourmaline was a desirable variety from the Tourmaline Queen Mine.
Dozens of Tourmaline mines have existed in Maine, since the gem’s discovery in 1820. Tourmaline could be found on Mt. Mica, at the Dunton Gem Pit, and the Havey Quarry.
The Dunton Gem Pit in Newry, Maine, is known as the largest single pocket of Tourmaline in the U.S. An estimated 2,000 kg of mineral specimens and rough were mined there between 1972 and 1974 in cranberry, pink, apple green, and bicolors.
The Havey Quarry in Poland, Maine, operated 1910–1912, with 7,000 carats of green Tourmaline cut from 25,000 carats of rough. The Quarry was reopened by Jeff Morrison in the early 2010s, leading to a successful run of mining since that time to the present day.
Turquoise is one of the oldest used gem materials in the world, found in ancient Egypt, the Persian Empire, and the Shang Dynasty of China. Turquoise has been mined in Arizona at the
Bisbee, Sleeping Beauty, Kingman, and Morenci sites and has been used by Native Americans for over a thousand years.
Quartz is perhaps the most common gem found in the U.S.—in 25 states! Colors include colorless and smoky brown.
There are many more lesser-known minerals that have been faceted found nationwide! I hope you enjoyed this roundup of some of the best-known ones.
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