Tourmaline October Alternate Birthstone
By Wayne Farley 2017
“Tourmaline( /ˈtʊərməliːn/ TOOR-mə-leen) is a crystalline boron silicate mineralcompounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-preciousstone and the gemstonecomes in a wide variety of colors. The name comes from the Tamiland Sinhaleseword "Turmali" (තුරමලි) or "Thoramalli" (තෝරමල්ලි), which applied to different gemstones found in Sri Lanka.”
The chemical formula for the most common variety of gem tourmaline, elbaite, is as follows: Na(Li,Al)3Al6Si6O18(BO3)3(OH)4
Tourmaline has a hardness of 7-7.5, a specific gravity of 3.02-3.28, and a refraction index of 1.616-1.662
Tourmaline is rarely florescent. Some dravite from Tanzania has been observed to fluoresce yellow to short-wave; some pink elbaite from Newry, Maine blue to short-wave; and some chrome-uvite from Africa red to short-wave and long-wave.
“There are many unique properties of tourmalines. First, they are piezoelectric which means that when a crystal is heated or compressed (or vibrated) a different electrical charge will form at opposite ends of the crystal (an electrical potential). Conversely if an electrical potential is applied to the crystal, it will vibrate. Secondly they are pleochroic which means that the crystal will look darker in color when viewed down the long axis of the crystal than when viewed from the side. This property goes beyond the idea that the crystal is just thicker in that direction. Even equally dimensioned crystals will demonstrate this trait. This property can be used as an advantage by gem cutters who may wish to enhance a crystal's pale color or weaken a strongly colored crystal.”
Tourmaline Gemstones: A good introduction to tourmaline, as a gemstone, can be found on the “Gemological Institute of America” (GIA) web-site at Ref-1. This site shows a total of 466 results for tourmaline. The introduction report from GIA is as follows:
“Tourmalines come in a wide variety of exciting colors. In fact, tourmaline has one of the widest color ranges of any gem species, occurring in various shades of virtually every hue. Many tourmaline color varieties have inspired their own trade names:
Rubelliteis a name for pink, red, purplish red, orangy red, or brownish red tourmaline, although some in the trade argue that the term shouldn’t apply to pink tourmaline.
Rubellite is one of tourmaline’s most sought-after and generally available colors.
Indicoliteis dark violetish blue, blue, or greenish blue tourmaline.
Paraíbais an intense violetish blue, greenish blue, or blue tourmaline from the state of Paraíba, Brazil, that contais copper.
Chrome tourmalineis intense green. In spite of its name, it’s colored mostly by vanadium, the same element that colors many Brazilian and African emeralds.
Parti-colored tourmalinedisplays more than one color. One of the most common combinations is green and pink, but many others are possible.
Watermelon tourmalineis pink in the center and green around the outside. Crystals of this material are typically cut in slices to display this special arrangement.
Cat’s-eye tourmaline:Some tourmalines also show a cat’s-eye effect called chatoyancy. Cat’s-eye tourmalines are most often green, blue, or pink, with an eye that’s softer and more diffused than the eye in fine cat’s-eye chrysoberyl. This is because, in tourmaline, the effect is caused by numerous thin, tube-like inclusions that form naturally during the gem’s growth. The inclusions are larger than the inclusions in cat’s-eye chrysoberyl, so the chatoyancy isn’t as sharp. Like other cat’s-eyes, these stones have to be cut as cabochons to bring out the effect.
Tourmalinated) Quartz: Black tourmaline (schorl) needles are quite common as inclusions in Brazil quartz crystals. They are often over 5 cm long, and pieces of tourmalinated quartz can weigh over 100 kg. Commercially large chunks of clear quartz with black tourmaline are broken down not with a hammer but by pouring boiling water on them to thermally crack the pieces into usable sizes. The usable pieces are then cut into cabochons.
In Montana, termalinated quartz crystals have been found at the P. C. Mine, Basin Creek, in Jefferson County.
Tourmaline Chemistry: A tourmaline’s chemical composition directly influences its physical properties and is responsible for its color. Tourmalines make up a group of closely related mineral species that share the same crystal structure but have different chemical and physical properties. They share the elements silicon, aluminum, and boron, but contain a complex mixture of other elements such as sodium, lithium, calcium, magnesium, manganese, iron, chromium, vanadium, fluorine, and sometimes copper.
Gemologists use a tourmaline’s properties and chemical composition to define its species. The major tourmaline species are elbaite, liddicoatite, dravite, uvite, and schorl.
Most gem tourmalines are elbaite, which are rich in sodium, lithium, aluminum, and sometimes—but very rarely—copper. They occur in granite-containing pegmatites, which are rare igneous rocks. Pegmatites are sometimes rich in exotic elements that are important for the formation of certain gem minerals. Pegmatites might contain very large crystals up to 1 meter (about 3 feet) in length. Because of the nature of pegmatites, different gem pockets within one pegmatite body can hold tourmaline crystals of very different colors. Or one pocket can produce a variety of differently colored tourmalines. As a result, many mines produce a variety of gem colors.
Another feature of gem pegmatites is the scattered distribution of pockets within them. For miners, working a pegmatite consists mostly of excavating barren rock until the work results in the occasional and sudden reward of a rich pocket full of spectacular gem crystals.
Elbaiteoffers the widest range of gem-quality tourmaline colors. They can be green, blue, or yellow, pink to red, colorless, or zoned with a combination of colors.
Liddicoatiteis rich in calcium, lithium, and aluminum. It also originates in granite-containing pegmatites and offers a diverse array of colors, often in complex internal zoned patterns. It’s named after the late Richard T. Liddicoat, former president of GIA and former chairman of its Board of Governors. He’s often referred to as the “Father of Modern Gemology.”
Uviteis rich in calcium, magnesium, and aluminum. Dravite is rich in sodium, magnesium, and aluminum. Both form in limestone that’s been altered by heat and pressure, resulting in marble that contains accessory minerals like tourmaline.
Some of the most important gem tourmalines are mixtures of dravite and uvite. They’re often brown, yellowish brown, reddish brown, or nearly black in color, but sometimes they contain traces of vanadium, chromium, or both. When present in the right concentrations, these impurities produce rich green hues that rival those of tsavorite garnet and, occasionally, even emerald. Dealers sell these gems as chrome tourmaline, even though they’re not always colored by chromium. The bright yellow gems some dealers call “savannah” tourmalines are also mixtures of dravite and uvite. Their coloring element is iron.
Schorlis typically black, and rich in iron. It forms in a wide variety of rock types. It’s rarely used as a gem, although it has been featured in mourning jewelry.
Tourmaline’s colors have many different causes. It’s generally agreed that traces of iron, and possibly titanium, induce green and blue colors. Manganese produces reds and pinks, and possibly yellows. Some pink and yellow elbaites might owe their hues to color centers caused by radiation, which can be natural or laboratory-induced.”
Gemstone Tourmaline Sources: “Although Brazil remains the most important source, commercially viable tourmaline deposits have been found in Afghanistan, Pakistan, Mozambique, Nigeria, Namibia, Tanzania, and the United States. The two principle sources in the United States are Maine and California.”
A special issue of the Mineralogical Record magazine covers several of the tourmaline mines in Maine and California, as well as tourmaline mines in Italy (Elba), Pakistan, and Nepal.
The abstract to the Maine MR-report states: “Granite pegmatites are the focus of mineral collecting activity in Maine; nearly half of all the species known from the state have been found in the pegmatites of Androcoggin, Oxford and Sagadahoc counties. Elbaite, the state gem, has remained Maine’s most sought-after mineral since its discovery at Mount Mica in 1820.”
The abstract to the California MR-report states: “The world-famous Himalaya mine was the world’s principal source of gem-grade and carving-grade tourmaline from its opening in 1898 until 1914. Today it is again producing fine gems and crystal.” Most of the mine’s production was purchased by the Imperial Chinese government as carving material. Chinese Dowager Empress Tz'u Hsi particularly liked the pink and red tourmaline and had the vast majority shipped to China from California mines. She had statues, bottles, sculptures, and jewelry made; most of which is lost now. The Boxer Rebellion and subsequent collapse of the government brought an end to this important market, and large-scale mining at the Himalaya mine ceased.
Tourmaline in Montana The five part series of binder reports on “Minerals of Montana” by Larry B. French, 2005-2009, list minor tourmaline occurrences in all of the western counties of Montana. The varieties are black Schorl or Dravite. No gemstone varieties are listed.
In Sept. 1978, a mining engineer student from Montana Tech, William Christopher van Laer, was searching for pegmatite crystals 1/4 mile north of highway 90 at Homestake Pass and discovered some excellent schorl tourmaline crystals in a new dig area. He published his experience in an article for the Lapidary Journal in the April 1979 issue. In the article several fist size black schorl specimens are shown with excellent luster and good terminations.
In 1997 Sinkankas references the Laer 1979 article and another Laer exploration project in the Homestake Pass area in 1985 (Sinkankas, Ref-7). Sinkankas states the following:
“W. C. Van Laer and others are actively exploring pegmatites in the Boulder Batholith in an area east of Butte in Jefferson County and they have discovered fine schorl crystals (Van Laer, 1979). Further investigations turned up colored tourmaline from a pegmatite in an area north-northeast of Butte (Van Laer, 1985). The tourmaline occurs as groups small prismatic crystals with green terminations and some crystals were purple or pink. None contained clear areas large enough to cut faceted gems but the outlook for fines of tourmaline, perhaps of gem grade, as well as other pocket minerals, is promising. As noted before, excellent gem quality smoky quartz and some topaz have been found and cut from these pegmatites.”
Another paragraph on schorl in the Boulder Batholith area from MinDad (Ref-3) is as follows:
“The area 10 miles east of Butte, in and around the Continental Divide, where the Homestake Pluton of the Boulder Batholith outcrops. Numerous aplites, grano-aplites, alaskaites are found throughout the area, and locally these bodies grade into coarse pegmatite. These are graphic granite pegmatites, marking the transition between fine-grained aplite and pegmatite and/or cavities. The Homestake Pluton is found in two separate units, both north and south of the pass (and the interstate highway). The pegmatites are characterized by the presence of boron, as indicated by tourmaline, axinite, and danburite. Tourmaline (schorl) is locally abundant (van Laer, 1979). Numerous pegmatite digs are visible from the road that goes from Homestake Pass to Delmoe Lake, but the specific area in question is restricted to an area roughly two or three miles around Homestake Pass”.
Details and a map to the above Homestake Pass – Delmoe Lake area can be found in the Falcon Field Guide “Rockhounding Montana”.
A schorl tourmaline crystal from the Homestake Pass – Delmoe Lake area that I purchased on eBay on 09/20/17 is shown below. The sheen is from micro matrix quartz, axinite, and mica in the schorl crystal groves.
Mineralogy & Geology of Tourmaline For general information on the mineralogy of tourmaline.
Gemstone Tourmaline Prices: “The prices of tourmaline vary tremendously, depending on the variety and quality. Most expensive are the Paraiba tourmalines, which may reach tens of thousands of dollars per carat. Chrome tourmalines, rubellites and fine indocolites and bi-colors may sell for as much as $1000 per carat or more. Other varieties are available for prices between $50-$750/carat, depending on the richness of the color”.
In my opinion, the best book to read as a buying guide for purchasing tourmaline gemstones is “Exotic Gems, Volume-3” by Renee Newman, 2014 (Ref-10). The book price is listed at $19.95, and can be purchased at most bookstores.
Another excellent recent gemstone buying guide is “Secrets of the Gem Trade” by Wise (Ref-18). However, this book is quite expensive at a list price of $ 99.95.
For high-end tourmaline gemstone prices, check out the “Heritage” or “Bonham” auction catalogs. The May 24, 2017 Bonham issue titled “Lapidary Works of Art, Gemstones, Minerals and Natural History” shows dozens of tourmaline gemstones with estimated values.
For low-end tourmalines prices, check out eBay on the net. However, be cautious, as some of those low prices may be because the gemstones are stimulants. There doesn’t appear to be any tourmaline synthetic (man-made) tourmaline on the market, as the tourmaline supply is quite prevalent.