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Black Tourmaline from Little Cahuilla Mountain by K. L. Gochenour 1988
Last Updated: 1st Jul 2009
See locality: Cahuilla District, Riverside Co., California, USA
This article was featured in the bimonthly magazine Rocks and Minerals, Vol. 63, No. 6, November/December 1988, p. 440-444.
© 1988 Kenneth L. Gochenour, Tustin, California. Used with author's permission.
Scenic overview of Little Cahuilla Mountain, Riverside County, California.
Location map showing Riverside County, California.Kenneth Gochenour
TOURMALINE, BERYL, SPODUMENE, QUARTZ CRYSTALS, AND ALBITE have been found as well-crystallized mineral specimens in the Cahuilla Mountain pegmatite district for over one hundred years. These occurrences are not well known, since as Sinkankas (1959) stated, "... the tourmaline mines ... are shrouded in mystery and their locations are far from certain." The recent discovery and marketing of excellent specimens of black tourmaline (schorl), quartz, and albite (variety cleavelandite) from Little Cahuilla Mountain add considerably to the importance of the district.
The Cahuilla Mountain district is located within the San Jacinto Mountain Range in Riverside County at an altitude of 3,000 to 5,000 feet. Most of the district, which consists of four mountains (Thomas, Cahuilla, Little Cahuilla, and Red mountains) is within the San Bernardino National Forest. The area is fairly desolate, with few roads, and is heavily vegetated by chaparral composed of scrub oak, greasewood, and chamise. Anza, the largest nearby town, has a population of twenty-eight hundred. The district is located on the Hemet and Idylwild 15' U.S. Geological Survey topographic maps.
Quartz and schorl crystals on microcline and perthite matrix. Largest crystal is 8 1/2 inches long.
Gem tourmaline (elbaite) was first found in California and in the Cahuilla Mountain district by Henry Hamilton, who found it in 1872 on Thomas Mountain (Kunz, 1905). Hamilton's gem mine later became known as the Columbia Gem mine; it has also been called the Belo Horizonte mine and the Desert Rose mine (Pemberton, 1983). Additional gem tourmaline discoveries were made in 1893 by Dwight Whiting, F. M. Speer, and F. H. Jackson, who mined red, green, and watermelon-colored elbaite from the San Jacinto Gem mine at an unspecified (and still unknown) location on the crest of the San Jacinto Range (Kunz, 1905). In the early 1900s, Bill McGee's father worked the Anita mine on the southwest slope of Red Mountain. He recovered many unusually large elbaite tourmalines. One crystal was reported as being so large that even though broken in half its termination alone would just fit into a coffee can.
In 1902, Burt Simmons of Oak Grove, California, founded the Fano-Simmons mine located on Cahuilla Mountain. He later sold the mine to Mr. E. A. Fano of San Diego for $1,250 (Rynerson, 1967). The mine became the foremost gem producer of colored (mostly blue and green) tourmaline, spodumene, beryl, and quartz crystals in Riverside County. It also produced lepidolite and amblygonite. In 1976, the Gochenours obtained a lease (which they still have) on the Fano-Simmons mine and started operations. They removed many pockets that contained quartz and aquamarine as single crystals and matrix specimens to 4 inches. In 1981, Bill McGee recovered excellent black tourmaline (schorl) crystals from the mine. Lustrous crystals up to 12 inches long from a pocket are in the Los Angeles County Museum. The Gochenours recovered three additional pockets of black tourmaline in 1982, 1983, and 1984.
In 1929, a long-time Riverside County prospector, Mr. Schindler, located what has become known as the Schindler group of claims on Little Cahuilla Mountain, about 3 miles north of the Fano-Simmons mine. These same claims were later relocated as the Silica-Beryl group in 1943 and exploited for radio-grade quartz crystals and beryl.
The first gem discovery on Little Cahuilla Mountain came much later. For nearly on hundred years the area was accessible only on foot or horseback. In 1953, a road was finally built to nearby Red Mountain. During the blasting of the roadbed on Little Cahuilla Mountain, a large pocket of quartz and aquamarine was opened that has been called the Hilton pocket. Although the Gochenours' work on Little Cahuilla Mountain started in 1980, only small amounts of well-crystallized pegmatite minerals had yet been found.
Author with first black tourmaline (schorl) crystal excavated from the pocket.
The Cahuilla Mountain district is dominated by the large Cretaceous-aged Coahuila Valley Pluton and Bautista Sill (Sharp, 1965) of quartz monzonite (adamellite), norite, and tonalite that have invaded the older, highly metamorphosed migmatitic schists, gneisses, and granites of the Bautista Complex.
The rocks of the Coahuilla Valley Pluton and Bautista Sill are found in contact with all the pegmatites in the district. In some of the more complex pegmatite dikes, schist is found on the hanging wall of the dikes as an inclusion with the norite. The pegmatites are typical of the batholith fringe pegmatites found throughout the southern California Peninsular Ranges.
Several major fault systems fringe Cahuilla Mountain. To the north is the northwest-southeast trending San Jacinto fault zone, and to the south is the similar trending Agua Caliente fault zone. Anza is located in a valley formed at the junction of two faults of the San Jacinto fault zone. Faulting has played a major role by uplifting the area and allowing erosion to expose the pegmatites in the Cahuilla Mountain district.
The pegmatites on Cahuilla Mountain are located on the eastern flank of the mountain. A steep-sided canyon created by the San Jacinto fault is covered with swarms of the pegmatites from which the tourmalines discussed here were removed.
Sketch of a cross section of the largest pocket showing the relative positions of the tourmaline and quartz crystals and the perthite and anhedral quartz matrix.
On New Year's Day, 1986, a large pocket in a pegmatite was taken from the slopes of Little Cahuilla Mountain. The pocket was found by carefully tracing float crystals that had eroded from the pegmatite. The pegmatite is exposed for 300 feet along a northwest to southeast strike and is 6 to 12 feet thick. It dips steeply to the east with no anticlinal rolls along the strike.
Black tourmaline (schorl) and quartz crystals were traced to a small buried section of pocket pegmatite* located in the center of the pegmatite. A "mineralized" fracture containing euhedral and etched crystal shards of quartz, albite, tourmaline, garnet, and microcline was found to enter the pocket pegmatite just below some large perthite blocks. Along this fracture, three small pockets of black tourmaline crystals with very complex second-order basal faces were removed. These pockets culminated in a fourth and larger pocket from which the best crystals were removed. The pocket was found just below the intersection of the perthite and quartz anhedrons (within the pocket pegmatite) that comprised the core of the pegmatite. When the pocket was first encountered, the feldspar began to fall away in thin slabs. The author has observed this to be a typical pattern that develops when uncovering a pegmatite pocket. The feldspar becomes splintery and etched directly adjacent to the pocket zones. As the feldspar is removed, the cavity entrance assumes an "A" shape. Albite-encrusted perthite fragments became more evident as did shards of quartz. At this point, doubly terminated quartz crystals up to 5 inches in length were encountered. As the pocket was excavated downward, its dimension enlarged until a red-brown clay was penetrated that was thoroughly packed with sections of black tourmaline. Several large quartz crystals and two 10-inch-across matrix specimens were removed from one wall of the pocket.
As the pocket was excavated further, the next crystals to make their debut were black tourmalines with complex terminations. Twenty or more crystals from 2 to 3 inches in length with r(1001) and o(2021) terminations and vertically striated sides were removed in rapid succession. At the very bottom of the pocket, encased in the red micaceous mud, were dozens of black tourmaline prisms from 6 to 9 inches in length; they were stacked on each other like cordwood but were broken into three pieces along their length. Each break had a distinctive feature; one was healed, the second, although sharp, was coated with a thin layer of a gray siliceous material, and the third was clean. The first two breaks probably occurred during pocket formation, but the third sharp fracture was not altered or mineralized. The sharp fracture was observed to extend right across the pocket; each tourmaline had the break in the same place. The pocket wall had a large fracture that was almost exactly in line with the fracture that was almost exactly in line with the fracture in the tourmalines. Subsequently, laumontite crystals have been found in some pockets. This is evidence of late-stage mineralization, possibly related to earth movement.
Close-up view of the excavated black tourmaline pocket cavity, which is 38 inches in diameter and 60 inches deep.Twenty pounds of quartz crystals, some with tourmaline crystals attached, and 35 pounds of tourmaline crystals were recovered from the pocket. Several orange-red to red-brown, etched spessartine garnets were found at the bottom of the pocket as well as some fine albite (variety cleavelandite) crystals. In total, 250 pounds of mud and crystals were removed.
This discovery has provided further evidence that the faulting and concurrent earthquakes are responsible not only for the attitude of the pegmatites on Cahuilla Mountain, but also for the breakage of the pocket contents.
Two hundred fifty finely terminated black tourmaline "thumbnails" as well as one hundred sharply terminated crystals to 3 inches were removed. Hundreds of pieces were carefully cleaned and reassembled. Many of the crystal sections were so badly broken that they could not be salvaged. Thirty crystals that were 6 inches or more in length were pieced back together.
Two very fine matrix specimens were reassembled. The first one was a large block of perthite feldspar covered with albite (variety cleavelandite) crystals and several 2-inch quartz crystals. Blossoming from one end of the specimen were four black tourmaline crystals 4 to 8 inches in length and 1/2 to 1 inch wide. The second fine matrix specimen was a plate 8 x 11 inches with smoky quartz crystals that were 1 x 3 inches, and a half-dozen black tourmaline crystals between 4 and 8 inches long radiating from the quartz crystals. These two fine groups are now on display at the San Bernardino County Museum in Redlands, Riverside County, California. Single crystals of black tourmaline from this pocket are currently available from several southern California mineral dealers as well as from the Gochenours.
Schorl and quartz crystals on a feldspar (albite) matrix. Largest tourmaline crystal is 9 inches long.
Access to the Cahuilla Mountain area is limited, as most of the undeveloped deposits are located on steep, heavily overgrown hillsides. Additional exploration will probably result in more discoveries of fine pegmatite minerals.
I would like to thank Mark I. Jacobson for his support, encouragement, and review of the manuscript.
*Pocket pegmatite, an informal term, typically occurs in the central part of many dikes in southern California. It is characterized by intergrown euhedral crystals of quartz, albite, potassium-feldspar, muscovite, lepidolite, spodumene, and tourmaline, with occasional clay-filled cavities containing gem crystals (Jahns, 1982).
Jahns, R. H. 1982. Internal evolution of pegmatite bodies. In Short course in granite pegmatites in science and industry. Winnipeg: Mineralogical Association of Canada.
Kunz, G. F. 1905. Gems, jewelers' materials and ornamental stones of California. Calif. Div. Mines Bull. 37.
Larsen, E. F. Jr. 1948. Batholith and associated rocks of Corona, Elsinore and San Luis Rey quadrangles, southern California. Geol. Soc. of Amer. Memoir 29.
Pemberton, H. E. 1983. Minerals of California. New York: Van Nostrand Reinhold.
Rynerson, F. 1967. Exploring and mining gems and gold in the West. Healdsburg, Calif.: Naturegraph.
Sharp, R. V. 1965. Geology of the San Jacinto fault zone in the Peninsular Ranges of southern California. Ph.D. diss., Calif. Inst. of Tech., Pasadena.
Sinkankas, J. 1959. Gemstones of North America. New York: Van Nostrand Reinhold.
This article was featured in the bimonthly magazine Rocks and Minerals, Vol. 63, No. 6, November/December 1988, p. 440-444.
© 1988 Kenneth L. Gochenour, Tustin, California. Used with author's permission.
Black Tourmaline from Little Cahuilla Mountain, Riverside County, California
Scenic overview of Little Cahuilla Mountain, Riverside County, California.
Location map showing Riverside County, California.
Kenneth Gochenour
2670 E. Walnut, Suite C
Tustin, California 92860
TOURMALINE, BERYL, SPODUMENE, QUARTZ CRYSTALS, AND ALBITE have been found as well-crystallized mineral specimens in the Cahuilla Mountain pegmatite district for over one hundred years. These occurrences are not well known, since as Sinkankas (1959) stated, "... the tourmaline mines ... are shrouded in mystery and their locations are far from certain." The recent discovery and marketing of excellent specimens of black tourmaline (schorl), quartz, and albite (variety cleavelandite) from Little Cahuilla Mountain add considerably to the importance of the district.
Location
The Cahuilla Mountain district is located within the San Jacinto Mountain Range in Riverside County at an altitude of 3,000 to 5,000 feet. Most of the district, which consists of four mountains (Thomas, Cahuilla, Little Cahuilla, and Red mountains) is within the San Bernardino National Forest. The area is fairly desolate, with few roads, and is heavily vegetated by chaparral composed of scrub oak, greasewood, and chamise. Anza, the largest nearby town, has a population of twenty-eight hundred. The district is located on the Hemet and Idylwild 15' U.S. Geological Survey topographic maps.
Quartz and schorl crystals on microcline and perthite matrix. Largest crystal is 8 1/2 inches long.
History of the District
Gem tourmaline (elbaite) was first found in California and in the Cahuilla Mountain district by Henry Hamilton, who found it in 1872 on Thomas Mountain (Kunz, 1905). Hamilton's gem mine later became known as the Columbia Gem mine; it has also been called the Belo Horizonte mine and the Desert Rose mine (Pemberton, 1983). Additional gem tourmaline discoveries were made in 1893 by Dwight Whiting, F. M. Speer, and F. H. Jackson, who mined red, green, and watermelon-colored elbaite from the San Jacinto Gem mine at an unspecified (and still unknown) location on the crest of the San Jacinto Range (Kunz, 1905). In the early 1900s, Bill McGee's father worked the Anita mine on the southwest slope of Red Mountain. He recovered many unusually large elbaite tourmalines. One crystal was reported as being so large that even though broken in half its termination alone would just fit into a coffee can.
In 1902, Burt Simmons of Oak Grove, California, founded the Fano-Simmons mine located on Cahuilla Mountain. He later sold the mine to Mr. E. A. Fano of San Diego for $1,250 (Rynerson, 1967). The mine became the foremost gem producer of colored (mostly blue and green) tourmaline, spodumene, beryl, and quartz crystals in Riverside County. It also produced lepidolite and amblygonite. In 1976, the Gochenours obtained a lease (which they still have) on the Fano-Simmons mine and started operations. They removed many pockets that contained quartz and aquamarine as single crystals and matrix specimens to 4 inches. In 1981, Bill McGee recovered excellent black tourmaline (schorl) crystals from the mine. Lustrous crystals up to 12 inches long from a pocket are in the Los Angeles County Museum. The Gochenours recovered three additional pockets of black tourmaline in 1982, 1983, and 1984.
In 1929, a long-time Riverside County prospector, Mr. Schindler, located what has become known as the Schindler group of claims on Little Cahuilla Mountain, about 3 miles north of the Fano-Simmons mine. These same claims were later relocated as the Silica-Beryl group in 1943 and exploited for radio-grade quartz crystals and beryl.
The first gem discovery on Little Cahuilla Mountain came much later. For nearly on hundred years the area was accessible only on foot or horseback. In 1953, a road was finally built to nearby Red Mountain. During the blasting of the roadbed on Little Cahuilla Mountain, a large pocket of quartz and aquamarine was opened that has been called the Hilton pocket. Although the Gochenours' work on Little Cahuilla Mountain started in 1980, only small amounts of well-crystallized pegmatite minerals had yet been found.
Author with first black tourmaline (schorl) crystal excavated from the pocket.
Geology
The Cahuilla Mountain district is dominated by the large Cretaceous-aged Coahuila Valley Pluton and Bautista Sill (Sharp, 1965) of quartz monzonite (adamellite), norite, and tonalite that have invaded the older, highly metamorphosed migmatitic schists, gneisses, and granites of the Bautista Complex.
The rocks of the Coahuilla Valley Pluton and Bautista Sill are found in contact with all the pegmatites in the district. In some of the more complex pegmatite dikes, schist is found on the hanging wall of the dikes as an inclusion with the norite. The pegmatites are typical of the batholith fringe pegmatites found throughout the southern California Peninsular Ranges.
Several major fault systems fringe Cahuilla Mountain. To the north is the northwest-southeast trending San Jacinto fault zone, and to the south is the similar trending Agua Caliente fault zone. Anza is located in a valley formed at the junction of two faults of the San Jacinto fault zone. Faulting has played a major role by uplifting the area and allowing erosion to expose the pegmatites in the Cahuilla Mountain district.
The pegmatites on Cahuilla Mountain are located on the eastern flank of the mountain. A steep-sided canyon created by the San Jacinto fault is covered with swarms of the pegmatites from which the tourmalines discussed here were removed.
Sketch of a cross section of the largest pocket showing the relative positions of the tourmaline and quartz crystals and the perthite and anhedral quartz matrix.
The Recently Discovered Pocket
On New Year's Day, 1986, a large pocket in a pegmatite was taken from the slopes of Little Cahuilla Mountain. The pocket was found by carefully tracing float crystals that had eroded from the pegmatite. The pegmatite is exposed for 300 feet along a northwest to southeast strike and is 6 to 12 feet thick. It dips steeply to the east with no anticlinal rolls along the strike.
Black tourmaline (schorl) and quartz crystals were traced to a small buried section of pocket pegmatite* located in the center of the pegmatite. A "mineralized" fracture containing euhedral and etched crystal shards of quartz, albite, tourmaline, garnet, and microcline was found to enter the pocket pegmatite just below some large perthite blocks. Along this fracture, three small pockets of black tourmaline crystals with very complex second-order basal faces were removed. These pockets culminated in a fourth and larger pocket from which the best crystals were removed. The pocket was found just below the intersection of the perthite and quartz anhedrons (within the pocket pegmatite) that comprised the core of the pegmatite. When the pocket was first encountered, the feldspar began to fall away in thin slabs. The author has observed this to be a typical pattern that develops when uncovering a pegmatite pocket. The feldspar becomes splintery and etched directly adjacent to the pocket zones. As the feldspar is removed, the cavity entrance assumes an "A" shape. Albite-encrusted perthite fragments became more evident as did shards of quartz. At this point, doubly terminated quartz crystals up to 5 inches in length were encountered. As the pocket was excavated downward, its dimension enlarged until a red-brown clay was penetrated that was thoroughly packed with sections of black tourmaline. Several large quartz crystals and two 10-inch-across matrix specimens were removed from one wall of the pocket.
As the pocket was excavated further, the next crystals to make their debut were black tourmalines with complex terminations. Twenty or more crystals from 2 to 3 inches in length with r(1001) and o(2021) terminations and vertically striated sides were removed in rapid succession. At the very bottom of the pocket, encased in the red micaceous mud, were dozens of black tourmaline prisms from 6 to 9 inches in length; they were stacked on each other like cordwood but were broken into three pieces along their length. Each break had a distinctive feature; one was healed, the second, although sharp, was coated with a thin layer of a gray siliceous material, and the third was clean. The first two breaks probably occurred during pocket formation, but the third sharp fracture was not altered or mineralized. The sharp fracture was observed to extend right across the pocket; each tourmaline had the break in the same place. The pocket wall had a large fracture that was almost exactly in line with the fracture that was almost exactly in line with the fracture in the tourmalines. Subsequently, laumontite crystals have been found in some pockets. This is evidence of late-stage mineralization, possibly related to earth movement.
Close-up view of the excavated black tourmaline pocket cavity, which is 38 inches in diameter and 60 inches deep.
This discovery has provided further evidence that the faulting and concurrent earthquakes are responsible not only for the attitude of the pegmatites on Cahuilla Mountain, but also for the breakage of the pocket contents.
The Crystals
Two hundred fifty finely terminated black tourmaline "thumbnails" as well as one hundred sharply terminated crystals to 3 inches were removed. Hundreds of pieces were carefully cleaned and reassembled. Many of the crystal sections were so badly broken that they could not be salvaged. Thirty crystals that were 6 inches or more in length were pieced back together.
Two very fine matrix specimens were reassembled. The first one was a large block of perthite feldspar covered with albite (variety cleavelandite) crystals and several 2-inch quartz crystals. Blossoming from one end of the specimen were four black tourmaline crystals 4 to 8 inches in length and 1/2 to 1 inch wide. The second fine matrix specimen was a plate 8 x 11 inches with smoky quartz crystals that were 1 x 3 inches, and a half-dozen black tourmaline crystals between 4 and 8 inches long radiating from the quartz crystals. These two fine groups are now on display at the San Bernardino County Museum in Redlands, Riverside County, California. Single crystals of black tourmaline from this pocket are currently available from several southern California mineral dealers as well as from the Gochenours.
Schorl and quartz crystals on a feldspar (albite) matrix. Largest tourmaline crystal is 9 inches long.
Conclusion
Access to the Cahuilla Mountain area is limited, as most of the undeveloped deposits are located on steep, heavily overgrown hillsides. Additional exploration will probably result in more discoveries of fine pegmatite minerals.
Acknowledgment
I would like to thank Mark I. Jacobson for his support, encouragement, and review of the manuscript.
Footnote
*Pocket pegmatite, an informal term, typically occurs in the central part of many dikes in southern California. It is characterized by intergrown euhedral crystals of quartz, albite, potassium-feldspar, muscovite, lepidolite, spodumene, and tourmaline, with occasional clay-filled cavities containing gem crystals (Jahns, 1982).
REFERENCES
Jahns, R. H. 1982. Internal evolution of pegmatite bodies. In Short course in granite pegmatites in science and industry. Winnipeg: Mineralogical Association of Canada.
Kunz, G. F. 1905. Gems, jewelers' materials and ornamental stones of California. Calif. Div. Mines Bull. 37.
Larsen, E. F. Jr. 1948. Batholith and associated rocks of Corona, Elsinore and San Luis Rey quadrangles, southern California. Geol. Soc. of Amer. Memoir 29.
Pemberton, H. E. 1983. Minerals of California. New York: Van Nostrand Reinhold.
Rynerson, F. 1967. Exploring and mining gems and gold in the West. Healdsburg, Calif.: Naturegraph.
Sharp, R. V. 1965. Geology of the San Jacinto fault zone in the Peninsular Ranges of southern California. Ph.D. diss., Calif. Inst. of Tech., Pasadena.
Sinkankas, J. 1959. Gemstones of North America. New York: Van Nostrand Reinhold.
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Locality Updated: San Miguel Mine, Moctezuma, Mun. de Moctezuma, Sonora, MexicoFrom David Von Bargen, 24th May 2013 23:52:46