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Information on Tourmaline
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Tourmaline

Tourmaline is a mineral that is complex in nature. Due to this complexity, it exhibits more range of color than any other mineral or gem (its closest competitor is corundum [sapphire/ruby]). A silicate mineral of reasonable hardness (approx. 7-7 1/2), the crystal form is hexagonal, but is most often seen as crystals of bulging triangular cross-section, with striations running the length of the crystals. If the crystals are doubly-terminated, usually one end will exhibit a predominately flat or basal termination, the other with a point (pedion termination faces). The crystals can grow stubby, but most often are elongated or pencil shaped.

The most commonly seen tourmaline is the sodium-rich black variety known as schorl. It forms in simple to complex granitic pegmatites. Iron is the primary coloring agent in this material. If the pegmatite contained lithium, manganese, and other rare elements, the colored varieties of tourmaline known as elbaite could form. Many elements can freely substitute for others in the tourmaline family. Elbaites often form beautiful crystals in colors of pink, red, green, blue, orange, yellow, or other shades, even colorless.

The different colors have sometimes been given identifying names of their own: indicolite for blue, rubellite for red, achroite for colorless, and sometimes the green is referred to as verdelite. Authorities occasionally get into a dispute over what actual color tones comprise these varieties. For example, rubellite originally meant bright red, like a ruby. Eventually pink tones were referred as rubellite often enough that it became acceptable to some authorities and not to others. Often colors shade from one hue to another, sometimes blending, sometimes remaining distinct. The color zoning can form both concentrically and longitudinal. The most common are those having a pink or red core and a green skin. They were nicknamed "watermelon" tourmaline because of the resemblance of the cross-sections to a slice of watermelon fruit. Sometimes crystals that started growing as schorl finished growing as elbaite, especially in pocket zones. These clay-filled bubbles in the granite formed when the rock was cooling, and contained the space necessary for gem crystals to form. If no pockets were present, the mineral is usually cracked and included ("frozen" into the quartz, feldspar, or mica) and most often not suitable for gemstones. The pocket material, on the other hand, is usually transparent, and sometimes "flawless". The pockets can also contain other exciting crystals and gems in addition to the tourmalines. As a matter of fact, gem pockets don't have to include tourmalines at all. Other gems found there can be beryls (aquamarines, heliodors, or most often morganites), topazes, apatites, smoky quartzes, lepidolite mica, spodumenes, and rare minerals such as herderite or beryllonite. An interesting aspect of the crystallization sequence in pockets mean that sometimes crystals, although not uncommon in themselves, rarely form in combinations. For example, aquamarines and heliodors (golden beryl) are rarely (if ever) found with elbaite tourmaline, but the pink or peach variety, morganite, is frequently associated. This is because too much iron present forms schorl, not elbaite, yet iron is the primary coloring agent in aquamarine and heliodor. Another example would be rose quartz, which although fairly common in pegmatites, is rarely found in combination with tourmaline or beryls for some reason. Crystals of schorl or elbaite can occasionally reach three foot long or more, although the average is much smaller. One very rare type of elbaite which has formed turquoise to electric blues in color, is due to inclusions of copper ions. It has so far only been found in a couple of mines in the state of Paraiba, Brazil, and is known in the trade as Paraiba tourmaline. Prices per carat can reach an astounding five figures.

Other types of tourmalines include liddicoatite, a rare multicolored gem variety so far found in Madagascar. It resembles watermelon elbaite in most respects. Also included are dravite and uvite. These are calcium-rich varieties found mostly in metamorphic rocks like marbles. Dravite is usually brown or black, but sometimes can form a yellow to green material that can be used as gems. Uvite is usually black, but can be other colors as well. It is seldom found in gemmy crystals. Buergerite is a bronzy-brown color variety found in rhyolite and has not been found in gem quality. The chemical composition is similar to schorl. A recently discovered variety, foitite (Gems and Gemology, Spring 1994), is also similar to schorl but lacks the sodium ions. Only a couple of non-gem bluish-black crystals have been discovered and came from southern California. An elbaitic tourmaline rich in the element bismuth has been discovered in Zambia (often reported to be from Mozambique). These are gem quality pink/green/black nodules, but so far there has been no attempt to declare these another variety.

One of the most exciting aspects of tourmaline is that it frequently forms spectacular and beautiful crystals, which pleases the mineral collector, as well as provides beautiful gemstones. Occasionally this creates a conflict: Do you sacrifice a rare crystal, beautiful in it's own right, to make a potentially even more valuable gemstone? My personal feeling is that there are plenty of damaged, chipped, broken or water-worn crystals and crystal sections to cut without sacrificing perfect crystals of great beauty or rarity. I realize there can be exceptions to this rule, but I think it's a good principle to live by.

What about tourmaline as a gem? Well, it's reasonably hard, has a moderate refractive index which give the cut stones warmth, and it comes in many colors. There is no cleavage to speak of, although crystals are often stressed perpendicular to the length, which can make cutting an adventure. If the colors are grayish and unsaturated or unpleasant, the stones are very inexpensive. If the colors are saturated and bright, they are very desirable and can get rather pricey. The most desirable colors include "Paraiba" blue; indicolite; teal; flawless watermelons or bicolors; rubellite; pink, especially "hot" pinks; chrome greens; and medium, bright greens. Like emeralds, moderate inclusions in some of the colors are considered acceptable, most notably hot pinks. Most bicolors are flawed also. Retail prices usually run from about $40 per carat to about $500 per carat, depending on color, clarity, and size, but can sometimes go considerably higher. Because of the crystal shapes they are found in, cut stones are often emerald cuts or the more elegant cushion cuts (especially the blues and greens). There are enough odd-shaped pieces found to supply most of the most common shapes however, such as rounds, pears, and ovals. The best color in pinks and rubellites is down the c-axis (unlike blues and greens) so they are less often cut into emerald cuts. Because of strong dichroism in the crystals, the color tones down the c-axis of many greens and blues are too olive, too dark (even black). The ends must be cut very steep on the pavilion to keep out this dark color. Round stones cut with this strong dichroism in them exhibit the famous "bowtie effect". This is sort of like an iron cross in shape, with one direction showing good color and the other direction showing poor color or no color at all. Like many gemstones on today's market, colors in tourmalines can sometimes be improved by heating or irradiating. Light pinks can go to rubellite red with irradiating, whereas dark stones of any color can sometimes be lightened to a more satisfactory saturation with heat. Heating does not always work for some reason though, and you always risk cracking the stones with this method.

Some of the many places good gem tourmaline has come from: the state of Minas Gerais, Brazil (all colors) is still the largest producer today. If you ever get a chance to read about the huge find of enormous cranberry rubellites at the Jonas Mine near Itatiaia, do so. It's a very fascinating story; Afghanistan (beautiful greens and blues, some pinks); Nigeria (large reds and pinks, greens); Madagascar, Mozambique, Zambia and many of the southern African countries (all colors); Namibia has produced some beautiful blues, teals, and reds in recent years; Tanzania has produced gem dravite: "pumpkin" orange, light green, yellow, and true chrome; Russia, China, Viet Nam, India, and Sri Lanka have produced minor amounts. Many of these localities have been written up at one time or another in GIA's publication, Gems and Gemology. Old copies of Mineralogical Record or Lapidary Journal, to name a couple of other sources can contain excellent articles on them as well.

In the U.S., the states of Maine and California are famous for tourmalines. In fact, the oldest operating gem mine in the U.S. was opened shortly after a discovery of gem tourmaline crystals entangled in uprooted tree roots around 1812 by the Hamlin brothers. This mine later became the Mt. Mica mine near Paris, Maine. Maine has produced many very fine gem crystals over the years. It is especially noted for particularly fine greens and blues, but some pink and watermelon has been produced. Most of the discoveries have been minor in size, but an enormous pocket of some of the finest watermelon crystals ever discovered was found in the early 1970's at Newry's Plumbago Gem Pit. The company that mined it, Plumbago Mining Co., also reopened the old Mt. Mica Mine recently, with light success. An historic old mine known as the Berry Mine was vigorously and enthusiastically worked recently by Stephen Welch with excellent success. Well, it was successful in recovering some nice gem tourmaline, but apparently not enough to make it viable for long.

California brought tourmaline to light as early as the turn of the century. Two mines are primarily responsible for its fame: the Stewart Lithia Mine at Pala, and the Himalaya Mine at Mesa Grande. The Stewart is especially famous for its crystals of "bubble-gum" pink tourmalines and good lapidary-grade lepidolite (pink to purple lithium mica). Some small greens of decent hue have been found, as well as bi-colors, grayish-blues, achroite, and a small area of true cherry red rubellite. The Himalaya is famous for burgundy tones, yellow-greens, flawless bi-colors, and many beautiful crystal specimens. The Tourmaline Queen Mine at Pala produced a few excellent pockets of large "hot pink", crystals with dark blue "caps", or flat terminations. Not a lot of gem material came from these, but the crystals are among the most beautiful in the world. The Pala Chief and a number of smaller mines have produced small amounts of pink and other colors, plus numerous gem beryls and gem spodumene (kunzite). The Little Three Mine at Ramona has produced dark greens and other tones in small quantities.

The Black Hills region of South Dakota has a large area containing pegmatites with tourmalines (as well as many other minerals). Unfortunately, pockets are almost non-existent. Scientists speculate that granites that form too shallow or too deep in the earth's crust tend to not allow the formation of gem pockets. But nice specimens of schorl are abundant here, and several mines produced a considerable quantity of specimen-grade elbaites, and an occasional gem piece.

Colorado has a mine complex near the Royal Gorge (Canon City) called the Mica Lode/Meyers Quarry that produced considerable gem tourmaline around the turn of the century. From what I have been able to gather, the tourmalines formed in a shear zone of some sort, rather than traditional pockets. Once this zone had been mined through, there were no more gems. Unfortunately, very few specimens from this locality remain that are properly identified, because many resembled gems from the California mining area. If any reader has pictures or more information regarding this area, I would be interested in hearing from you.

Tourmaline xl before cutting, reported to be from Canon City.

Another pegmatite region near Ohio City (Gunnison County) contains a few mines with elbaite, the most famous of which is the Brown Derby Mine. This is another unpocketed area though, so gems are basically non-existent from here. Material comes in many colors, including considerable watermelon, pink, green, yellow, blue, and purple, but most has a strange waxy appearance. A few pieces will cut interesting cabs. There are rumors of other "lost" elbaite areas in the state. However, for as much granite and pegmatite as there is exposed here, tourmaline is surprisingly rare.


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