are arguably one of the most popular gemstones ever discovered. Originally
native to Sri Lanka, significant finds have recently been made across Europe,
Africa and South America depicting the inherent multiplicity of this mineral
species. With a wide array of dazzling color variations that span from black,
red, and pink, to even peach, tourmalines have become an international favorite
for many jewel lovers. In particular, the blue-green copper-bearing
Paraiba-type is one of the most noticeable and highest priced gems from the
tourmaline family with quality specimens fetching as much as $300 and $600 per
carat (“Paraíba Tourmaline Value,
Price, and Jewelry Information,” n.d.).
Demand for tourmaline was notably significant during the Second World War
(1939-45) since it was an integral component in the development of war-time
equipment such as submarine pressure sensitive gauges. Later on, tourmalines
encountered a receptive environment that bolstered its popularity and
permeation across the globe.
Color Producing Mechanism
Tourmalines exhibit an extensive range of colors. Typically, specimens may be black, red, pink, yellow, blue, green or even multicolored. In essence, this kaleidoscope of colors is a reflection of the chemical interactions that have taken place in the gemstone at specific structural levels. Commonly referred to as the inter-valence charge transfer interactions (IVCT) and the rare crystal field transitions (CFT), these primary causative agents are the main color producing mechanisms. Transition elements such as ferrous ions, manganese (II) ions, titanium (4+) ions, cupric ion, and vanadium 3+ ions are some of the most notable color-causing agents. Commonly referred to as chromophores, they are located in the Y and Z segment of the octahedral sites and responsible for the color intensity evident in the gem. In addition to this, natural irradiation is also a chief factor in the enhancement of these naturally occurring colors. Decaying isotopes (markedly 232Th, 40k, and 238U) may be found close to sites rich in tourmaline inadvertently influence the gem’s color.
other instances, tourmaline may present chatoyancy. In this particular state,
the gem scatters parallel bundles of light rays hitting it and ultimately
aligns it with its c axis. It is, however, vital to acknowledge that the
intensity of this spectacle is dependent upon the dimension and density of the
tubes located in each crystal. Nevertheless, changing conditions have also been
extensively explored as crucial factors for consideration when examining the
tourmaline color producing mechanism. According to Klein & Philpotts (2016), changes that occur during the crystals development may
result in any of the different colors observed in various tourmaline species
(183). During its nascent growth period, a color may overgrow and result in
bicolor crystals with a series of zones through its cross-section. Through such an intricate mechanism,
collectors have been successful at amassing some of the most desirable
specimens that also happen to be novelty samples.
Physical Variations and Production
The variation observed in the physical differences of separate tourmaline species is as a result of the gem’s elaborate chemical makeup. In all, there are 30 unique tourmaline species, with each being a discrete derivative of the XY3Z6 (T6O18) (BO3)3V3W chemical formula (Dietrich, 2012). Each has the same chemical structure, even though their internal elements may vary from one species to another. Colors transition from the more common deep-green right through to the rare deep-red as the light wavelength increases. Aptly dubbed the “Usambara effect,” the physical variations are attributes of various spectral positions in specific ratios during transmission.
Even so, all versions of the gemstone occur in metamorphic and igneous rocks. Achroite is the rarest of the Elaite tourmaline gem variety and colorless. Another scarce individual is the bronze-like buergerite tourmaline that was first discovered in 1966 by exploration geologists in San Luis Potosí, Mexico. Columnar aggregates result in the production of three-sided prisms that develop growth layers over time. Dravite tourmaline is rich in sodium magnesium, hence its brown color, though color variations also exist in this species. They may appear as Indicolite (blue tourmaline), Siberite (scarlet-violet tourmaline), Rubellite (red tourmaline), Watermelon tourmaline (iridescent pink) and Paraiba (blue-green tourmaline). Physical variations also extend to the Elaite tourmaline group well-known for its value. Traces of impurities found in the crystal tint the gemstone, making it allochromatic, although it can also appear pleochroic. Multi-color zones are, thus, common here giving the gem a rainbow allure. Final products often acicular inclusions that are microscopically resulting in the infamous cat eye effect. Schorl tourmaline represents the only black variation in the group while color zoned liddicoatite are produced against a backdrop of parallel pyramid faces.
Crystal Structure and Molecular Composition
Uses of Tourmaline
has soared over the past two decades. It is now commonplace for buyers to part
with a substantial amount of money to obtain these rare natural specimens. Even
so, buyers still purchase this rare gem for a range of reasons.
tourmaline is commonly cut into various styles and used as jewelry gemstones.
Its wealth of colors has made it a favorite for many collectors since buyers
have a wide array of colors from which to choose from. Its aesthetic value has
made it the most prized gem in the mineral kingdom and still reigns supreme
owing to its magnificent beauty. Tourmaline gems are never identical, a factor
that contributes to its general appeal and demand among collectors. Tourmaline
is fashioned into bracelets, necklaces, rings, and pendants that are worn by
its admirers across the globe.
Secondly, tourmaline acts as an electrical
conductor when heated. This is because it is piezoelectric, enabling it to hold
electrical charges once heated and consequently cooled. Experts specializing in
the minerals uses have harnessed its unique characteristics and now use it in
blow dryers and hair straighteners. The negative ions produced once it is
heated reduce fizz which then shields the hair from heat-induced damage. Adding
the mineral to blow dryers results in the discharge of more ions while
remaining light and manageable.
Thirdly, tourmaline is a polarizing device. Cutting
the mineral along two opposite axes allows it to act as a device capable of
blocking light and the reason why manufacturers use it to build tongs.
Moreover, this particular attribute can also be used in concert with its
ability to conduct electricity resulting in a device for measuring and
monitoring pressure changes. Gauges have
benefitted the most from the incorporation of this particular gemstone.
Temporary spikes in pressure can now be easily detected, thus improving
Tourmalines represent an exclusive class of
semi-precious minerals famed for their striking glamour and beauty. They
include elements such as lithium, magnesium, aluminum, sodium, and iron which
influences its color. As a result, a broad spectrum of colors ranging from
black, red, pink, yellow, blue to green. These colors are usually as a result
of the chemical interactions occurring in the gemstone at a structural level.
The inter-valence charge transfer interactions (IVCT) and crystal field
transitions (CFT) are the two predominant color producing mechanisms. The
tourmaline group includes gemstones with a wide range of variations due to its
elaborate chemical makeup. These dissimilarities have allowed experts to
fashion the gem into various pieces of jewelry, use it as an electrical
conductor and also as a polarizing device.