Hiddenite: North Carolina's Unique Gem

by

Margaret W. Martin

http://www.emporia.edu/earthsci/amber/go340/martin

This webpage project was created for a gemstones and gemology course in the 2010 spring semester at Emporia State University. The assignment was to learn webpage creation as well as present a summary of the gem, hiddenite.

Table of Contents
Introduction Spodumene Varieties
Hiddenite Occurrence Hiddenite Discovery and Mining
Faceting Challenges Hiddenite Collections
Conclusion References

Introduction

The discovery of hiddenite, a rare gem variety of the mineral spodumene, brought fame to its discoverer and a flurry of mining operations to rural Alexander County, North Carolina in the the late 1800s. Prior to the discovery of hiddenite, western North Carolina was already of interest to prospectors seeking emeralds and other gems. Although other gem varieties of spodumene have been discovered throughout the world, this report will focus on the occurrence, discovery and mining history of the hiddenite gem in North Carolina. Hiddenite's faceting challenges and notable hiddenite collections will also be discussed.

Warren Farm hiddenite. Mineral and Lapidary Museum of Henderson County,
Hendersonville, North Carolina Photograph by W. E. Speer, used by permission

Spodumene Varieties

The mineral spodumene is a lithium, aluminum silicate. Spodumene crystals are often large, and belong to the monoclinic crystal system. The mineral has a perfect prismatic cleavage with an uneven fracture. Spodumene has a specific gravity of 3.1 to 3.2, and a hardness between 6.5 and 7. It has a pearly to vitreous luster, and is found in a variety of colors. The common white and gray colored spodumene is a main source of lithium. Additional colors of the mineral include green, lilac, pink and purple. (Stuckey, 1965, p. 483).

Color determines the varieties of spodumene. The name for colorless to yellow spodumene is triphane. Pale, yellowish-green spodumene has no particular varietal name. Hiddenite and kunzite are the best known transparent gem varieties of spodumene. These richly colored varieties are faceted into gems, and hiddenite crystals are popular with collectors and museums. Hiddenite is an emerald-green gem variety found in North Carolina. Kunzite is a beautiful pink to violet gem first discovered near Pala, California in the early 1900s. It was named for Dr. George F. Kunz, a famous U. S. mineralogist, and, at the time, Vice President of Tiffany's of New York. More than twenty years before kunzite was found, the rare emerald-green hiddenite had been discovered in North Carolina. The gem was named for W.E. Hidden, who found the variety while searching for emeralds (Sinkankas, 1959, pp 150-155).

The hiddenite variety of spodumene is unique because it is found only in a small geographic region of North Carolina, and also because it receives its intense color from chromium, the same element that gives emerald its deep green hue. Unlike kunzite, whose color will fade in daylight over time, hiddenite’s color will remain stable when subjected to intense heat or light.

Natural hiddenite. Photograph
from www.ncmarkers.com/
marker_photo.aspx?sf=c&
id=M-29
. (North Carolina
Department of Cultural
Resources, 2010).

A blowpipe flame will cause the gem to lose color when hot, yet the gem’s deep, original color will return when it is cold. This property is seen in ruby and emerald; gems that also receive their color from chromium. Chromium is usually not present in other spodumene localities (Sinkankas, 1959, pp 150-155). Specimens from other localities claiming transparent, green spodumene do not have the same unique green color found in the variety from the hiddenite district of North Carolina. Green spodumenes from other localities outside of Alexander County, North Carolina are usually a very light green or greenish-yellow color, and although gem dealers sometimes label these gems as hiddenite, they are not gemologically acknowledged as true hiddenite (minerals.net, 2003).

Technically, hiddenite refers to the variety of spodumene having a permanent deep green color, due to the detectable presence of trace amounts of chromium. Dealers claiming to have hiddenite from other locations usually possess the less rare, light green varieties, with no documentation that chromium is present. Spodumene is a mineral that is sometimes heat treated in order to change the color to a green shade, even if no chromium is present. In some heat-treated specimens from other locations, the green color is known to fade or disappear over time, or with exposure to sunlight. Verified hiddenite, the spodumene variety with a permanent, natural deep green color, is found only in Alexander County, NC. The hiddenite found there has been tested and shown to contain chromium (P. Potter, 2010, personal communication).

Hiddenite Occurrence

Spodumene is found in granitic pagmatites. In North Carolina, a pegmatite belt, the Kings Mountain Tin-Spodumene Belt, extends from the South Carolina line and crosses three south central North Carolina counties; Cleveland, Gaston and parts of Lincoln County. The gem hiddenite was discovered in 1879, north of the Kings Mountain pegmatite belt, in Alexander County, near the present community of Hiddenite. (figure 1) (Stuckey, 1965, p. 483).

Figure 1 - Hiddenite Region of North Carolina; (Adapted from Brown, 2001).

Alexander County, North Carolina is part of the western Appalachian Piedmont and lies between the Atlantic Coastal Plain and the Blue Ridge Mountains. The rocks underlying the Piedmont province form parallel geologic terranes running northeast to southwest. The Piedmont province, an ancient erosional surface, is underlain by metamorphosed late Precambrian to early Paleozoic age rocks. Triassic sediments have filled downfaulted basins in the area, and gabbroic dikes and sills have intruded the Triassic sediments (Brown and Wilson, 2001).

Hiddenite is found in an area of Alexander County called the Hiddenite District (figure 2). This ten square kilometer district is not only the discovery site of the gem hiddenite, but also the location of North America's largest and finest emerald deposits. The Hiddenite District is the only place in the world where emerald and hiddenite occur together naturally. The host rocks underlying the region have undergone complex deformation. The Hiddenite District lies within the Inner Piedmont terrane, an exotic mass of rock that collided, about 350 years ago, with the North American craton. Subsequent collisions occurred when the Carolina terrane to the east was accreted to the Inner Piedmont, causing more deformation of the underlying rocks. The host rocks of the district are mainly migmatitic biotite gneiss which are cross cut by hydrothermal, Alpine-type quartz veins. The quartz veins are thought to be tensional fractures that formed during late metamorophic deformation of the host rock. Emerald crystals and other associated mineral crystals, such as hiddenite, are found in open cavities of the quartz veins (Speer, 2009).

Figure 2 - The Hiddenite District (Speer, 2009).

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Hiddenite Discovery and Mining

The agricultural community of Stony Point, North Carolina was so named due to the prevalence of stones with points found in nearby plowed fields. In the mid-nineteenth century, green stones, locally called green bolts, were often noticed in the farmers' fields. Residents thought the stones were green glass, made by lightning fusion with the red soil. A mineral collector and nearby merchant, John A. D. Stephenson, began buying the green stones from local farm families and soon realized the stones were emeralds. The James Warren farm of Alexander County, now known as the Adams property, was the site of the earliest discoveries. It was at this location Stephenson was introduced to a unknown green mineral he originally thought was diopside. Samples were submitted to a mineralogist in Pittsburgh, Pennsylvania, but a final identification was never accomplished from this source.

Later, William Earl Hidden, a mineralogist who traveled to North Carolina for Thomas Edison to seek out platinum sources for the electric light bulb, visited Stephenson to view his collection of minerals. After visiting the Warren farm with Stephenson, W. E. Hidden decided to lease the farm for mining emeralds. Hidden established the Emerald and Hiddenite Mining Company in 1880 and mined it until 1888. During this time the mine produced many fine emerald specimens, two earning the distinction of North Carolina's largest emeralds at that time. Hidden also uncovered many specimens of the green crystals that had been previously labeled diopside. These mysterious crystals were sent by Hidden to J. Lawrence Smith in 1881, who identified the crystals as a chromium green variety of spodumene. The newly identified mineral was named hiddenite because W. E. Hidden had submitted them. This new mineral brought fame to Hidden and to North Carolina. A mail stop near Hidden's mine became known as Hiddenite and a new town nearby also took on the name Hiddenite. William Hidden's new spodumene variety and the emeralds were in great demand. Faceted hiddenite gems sold at $850 to $5,300 a carat (2008 U.S. dollar value), and the total emerald and hiddenite production value of the mine in eight years yielded approximately $176,000 (2008 U.S. dollars) The Emerald and Hiddenite Mining Company eventually closed in 1888 due to property issues and the lack of new emerald discoveries (Speer, 2009).

Subsequent mining attempts for hiddenite and emerald were made at Warren property and properties nearby. Prospects west and east of Hiddenite yielded both emerald and hiddenite around 1907. The Ellis property east of Hiddenite yeilded 200 carats of hiddenite crystals and a 276 carat dark green emerald was also uncovered (Brown, 2001). Mr. Burnham S. Colburn leased the Hiddenite mine in 1926. He was interested in hiddenite because of its rarity, not its value. Mr. Colburn helped start the Southern Appalachian Mineral Society and was the founder of the Colburn Gem and Mineral Museum in Asheville, North Carolina. Colburn collected many fine hiddenite specimens during his short history of mining the mineral, and many specimens from his large collection were given to museums throughout the world (Presnell, 1999, p. 35).

Another spurt in mining in the area occurred in the 1970s when the former Hiddenite mine was a prospect-for-fee mining operation. Many valuable discoveries were uncovered, including a 1,493 twin emerald crystal, found by Robert Reitzel, which currently holds the place as the third largest emerald in North America. As of 2001, a tract known as the Wooten-Rutledge mine, had uncovered hiddenite veins that produced over 800 specimens (Brown, 2001). Currently, the North American Emerald Mine, formerly the Rist Mine, is being commercially mined. The operation produces emeralds and crushed-stone aggregates. The significant discoveries at this mine are mostly emeralds, including, in 2003, the largest emerald crystal found to date in North America. It is 1,869 carats, valued over one million dollars, and displayed at the Houston Museum of Natural Science. The Adams Mine, the old Emerald and Hiddenite Mine, is currently leased and worked by Terry Ledford. Recently, valuable hiddenite specimens have been uncovered there. Estimates from public and private sources have indicated that, from 1880 to 2007, the entire Hiddenite District has produced about 20,000 carats of hiddenite and 70,000 carats of emerald (Speer, 2009). For more information about the hiddenite and emerald mines of the Hiddenite district visit North Carolina Emeralds, www.northcarolinaemeralds.info/.

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Faceting Challenges

Hiddenite crystals have an unmistakable appearance. Sinkankas (1959) described the shape of a hiddenite crytal as similar to a minature Roman sword, with a handle on one end, and a thicker, pointed end at the crystal's termination. The gem's richest green color is near the termination, which is also the most flawless part of the gem. The crystal sides usually exhibit grooves which run parallel to the crystal's length.

The rich, transparent, green colored hiddenite from Alexander County can be fashioned into beautiful gems, but the stone's perfect cleavage and splintery fracture make hiddenite very difficult to cut. The gem will also chip if it receives a hard hit. The deeper green colors are more valuable, and due to the gem's strong pleochroism, it is advisable to cut the stone in a manner that displays the deepest color through the top of the gem (minerals.net, 2003). When properly cut, hiddenite can be brilliant, but the mineral's low dispersion (0.017) causes the stones to have little fire. Hiddenite's definite pleochroism shows colors ranging from bluish-green, emerald green to yellowish-green. In order to fashion a hiddenite gem of optimum color, the gem's table should be perpendicular to the c-axis, insuring that facet angles less than 90 degrees will not be parallel to the cleavage plane. Since most crystals are long and thin, it is difficult to cut them into large stones with the best color (Bradshaw, 1993).

Hiddenite, Robert Reitzel exhibit at Unifour Gem, Mineral and Jewelry Show.
Photograph by Margaret W. Martin

Hiddenite Collections

Notable hiddenite crystals and gems have been collected by the persons associated with the mining operations, and many of these specimens have been sold to private collectors or donated to museums. The British Museum in London, the American Museum of Natural History in New York, Harvard, and the Smithsonian Institution in Washington, D.C. are examples of museums displaying fine hiddenite specimens (Pough, 1993). In North Carolina and South Carolina, hiddenite collections are held at Belmont Abby College in South Carolina, the McKissick Museum at the University of South Carolina, the Colburn Earth Science Museum in Asheville, North Carolina, and the North Carolina Museum of Natural History in Raleigh. The North Carolina Museum of Natural History recently purchased a collection from North Carolina collector, Paul Tucker. One of these pieces is a historically significant crystal that originally belonged to William Hidden. Hidden had inserted this small crystal into his business card to display to business associates, and it is still in Hidden's card. Burnham Colburn sold the best of the hiddenite he discovered to the Smithsonian, and to the McKissick Museum at the University of South Carolina. Some of the best crystals in the Colburn Earth Science Museum in Asheville, North Carolina are also from Burnham Colburn. These were found by Burnham and William Colburn when they mined the original Emerald and Hiddenite Mine from 1926 to 1927. A high quality, small faceted hiddenite that George Kunz had cut in the late 1800s, is a very significant part of the hiddenite exhibit at the Colburn Museum (P. Potter, 2010, personal communication).

Above left: William Hidden's 1905 business card displaying a hiddenite crystal (North Carolina Museum of Natural Sciences, 2005.). To view Treasures Unearthed, North Carolina's spectacular gems and minerals, a Rockhound's Guide to selected specimens go to Rockhound's Guide, naturalsciences.org/files/documents/rockhounds_guide.pdf. For an interactive exhibit see treasures, naturalsciences.org/microsites/exhibits/treasures/TREASURESPROJECT/index.htm.

Above right: Hiddenite crystals: Colburn Earth Science Museum, Asheville, North Carolina. Photograph by W. E. Speer, used by permission.

Conclusion

Hiddenite, a rare gem discovered in 1879 in Alexander County, North Carolina, brought fame and prosperity to the rural region. The gem continues to be treasured by gemologists, mineral collectors and museums because of its rarity, its uniquely American identity, and its unusual, tranparent green colors. The hiddenite occurrence in North Carolina is significant because it is found only in a small region of the North Carolina western Piedmont, and is found in association with emerald. Many small scale hiddenite mining ventures have been pursued sporadically since 1880, and those in operation today are still producing remarkable specimens.

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References

Brown, D. and Wilson, W. 2001. The Rist and Ellis Tracts, Hiddenite North Carolina. The Mineralogical Record, 32, p. 132 - 140.

Bradshaw, John J. 1993. Faceing Hiddenite. Lapidary Journal, February 1993, p. 107 - 108.

Minerals.net. 1997 – 2003. World Wide Web homepage < www.minerals.net/gemstone/gemstone/hiddenit/hiddenit.htm> [retrieved on 27 April 2010].

North Carolina Department of Cultural Resources. 2010. North Carolina Highway Historical Marker Program. World Wide Web homepage [retrieved on 26 April 2010].

North Carolina Museum of Natural Sciences. 2005. Treasures Unearthed, rockhound's guide to selected specimens. World Wide Web homepage [retrieved on 26 April 2010].

Potter, Phillip M., MS, PG, Curator, Colburn Earth Science Museum. 2010. Personal communication, 7, May, 2010.

Pough, Frederick H. 1993. Speaking further of spodumene. Lapidary Journal, March 1993, p. 14, 90 - 91.

Presnell, Lowell. 1999. Mines miners and minerals of western north carolina. Parkway Publishers, Boone, North Carolina, 256 p.

Sinkankas, J. 1959. Gemstones of North America. D. Van Nostrand Company, Inc., New Jersey

Speer, W. E. 2009. North Carolina famous for North America's largest emeralds. Mining Engineering. June, 2009, p. 83 - 87.

Speer, W. E. 2010. North Carolina Emeralds. World Wide Web homepage [retrieved on 26 April 2010].

Stuckey, Jasper I. 1965. North Carolina: Its Geology and Mineral Resources. Department of Conservation and Development, Raleigh, NC


About This Webpage

This website was created by Margaret Martin, May 2010. It fulfills an assignment for a graduate gemstone and gemology course from Emporia State University, Earth Science Department,
http://www.emporia.edu/earthsci/earthsci.htm. For questions and comments, email mmartin6@emporia.edu. Online May 11, 2010.

Return to other student webpage examples at www.emporia.edu/earthsci/amber/go340/students/stupages.htm.