Taos Rockers
229 A Camino de la Placita, Taos, NM, 87571
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Tos Rockers' Mineral of the Month Blog

Typically each month, a mineral is showcased in our storefront as our Mineral of the Month. Come in to check out our display of the wide variety of differences found in the mineral due to localities in which it is found, as well as the different habits that the mineral takes on. Here, on our blog we present you with a write-up of information along with pictures showcasing each mineral chosen. We encourage and welcome your input! At the bottom of each page you will find a comments section. Happy sharing!

 

June - Tourmaline

MINERAL OF THE MONTH – TOURMALINE

Verdelite

Verdelite

Rubellite

Rubellite

Taos Rockers mineral of the month is Tourmaline.  The name "tourmali" was a generic name used in Ceylon [Sri Lanka] for colored gems, mostly zircons. About 1703, it had been discovered by Dutch lapidaries that some of the "zircons" arriving in the Netherlands were actually a previously undescribed mineral.  Tourmalin, as a more or less specific mineral name, was used by Rinmann in 1766. Hill called it Tourmaline Garnet in 1771 and Richard Kirwan shortened the name to "Tourmaline" in 1794.

 

·  Mineral: Tourmaline

·  Chemistry: A(D3)G6(Si6O18)(BO3)3X3Z 

            where A = Ca, Na, K, or is vacant (large cations);
            D = Al, Fe2+, Fe3+, Li, Mg2+, Mn2+ (intermediate to small cations - in valence balancing combinations

                        when the A site is vacant);
            G = Al, Cr3+, Fe3+, V3+ (small cations);
                        Si can sometimes have minor Al and/or B3+ substitution.
            X = O and/or OH
            Z = F, O and/or OH.

·  Class: Cyclosilicate (Trigonal borosilicate)

·  Crystal system: Hexagonal

·  Color: Most commonly black, but can range from colorless to brown, red, orange, yellow, green,           blue, violet, pink, or hues in between; can be bi-colored, or even tri-colored; rarely can be neon green or electric blue

·  Refractive index:  1.610 – 1.675

·  Luster: Vitreous, sometimes resinous

·  Specific gravity: 2.9 - 3.1

·  Mohs Hardness: 7

·  Cleavage: Indistinct

·  Fracture: Uneven, small conchoidal, brittle

 

Dravite

Dravite

Due to the vast combinations of elements that can occupy positions in the crystal lattice, Tourmaline is often referred to as a garbage can (or kitchen sink) mineral.  Thirty-three "pure" combinations have been identified and given specific names as varieties of the Tourmaline group by the International Mineralogical Association.  There is also a list of trade names for Tourmaline based upon color or color combinations ("color name").. 

 

It can be impractical to impossible to determine the chemical composition of the various specimens in the field, classroom, office, or laboratory, hence the generic name "Tourmaline" is used for any mineral in the tourmaline group.

Watermelon Tourmaline; Rubellite, Verdelite

Watermelon Tourmaline; Rubellite, Verdelite

Bicolor Tourmaline; Indicolite, Verdelite

Bicolor Tourmaline; Indicolite, Verdelite

 

One factor in Tourmaline's popularity as a gemstone is that it occurs in every color - it has one of the widest color ranges of any gem species.  To aid in discussions between the public and jewelers or gemologists a trade name based on the color of tourmaline is used:

Schorl            black; Sodium/Iron rich; most common species of tourmaline, 95% or more

                        of all tourmaline in nature

Elbaite           Sodium/Lithium rich; offers the widest range of gem tourmaline colors

                        red or pinkish red - Rubellite (Lithium rich)

                        light blue to bluish green - Indicolite

                        green - Verdelite

                        pink core & green rim - Watermelon

                        colorless - Achroite

Liddicoatite blue; Calcium/Lithium rich

Dravite           brown tourmaline; Sodium/Magnesium rich

Paraiba          intense greenish/bluish; colored by presence of Copper

 

Physical properties of Tourmaline useful in identification of the mineral include

* a prismatic crystal habit typically with striations parallel to the long axis of the crystal

* a triangular or 6-sided cross-section with rounded edges

* often color zones through their cross-section or along their length

* can be pleochroic - darkest when viewed down the c-axis, lighter when view perpendicular to the c-axis

* indistinct cleavage

Tourmaline is a six-member ring cyclosilicate having a trigonal crystal system. It occurs as long, slender to thick prismatic and columnar crystals that are usually triangular in cross-section, often with curved striated faces. The style of termination at the ends of crystals can be different at opposite ends, called hemimorphism. All hemimorphic crystals are piezoelectric, and are often pyroelectric as well

Tourmaline is a common constituent of granite and granite pegmatites, and can be found in hydrothermal veins and in metamorphic rocks.  Schorl and lithium-rich tourmalines are usually found in granite and granite pegmatite. Magnesium-rich tourmalines are generally restricted to schists and marble. Due to its hardness and relative resistance to chemical weathering, Tourmaline can be transported by water long distances from their source area as alluvial deposits.  Tourmaline typically occurs as an accessory mineral.  Large, well-formed crystals of tourmaline can form in cavities and fractures during hydrothermal activity.

The primary use of tourmaline in general is as a semi-precious gemstone.  Tourmaline is a birthstone for the month of October and the gemstone of the 8th Anniversary.

Gem and specimen tourmaline is mined chiefly in Brazil (the world's leading source of tourmaline for nearly 500 years) and Africa. Some placer material suitable for gem use comes from Sri Lanka. In addition to Brazil, tourmaline is mined in Tanzania, Nigeria, Kenya, Madagascar, Mozambique, Namibia, Afghanistan, Pakistan, Sri Lanka, and Malawi.   In the United States, fine gems and specimen materials have been produced in Maine and San Diego County, California.

Some of the locales from which specimens of Tourmaline are available at Taos Rockers are:

California                  Afghanistan              China

Idaho                          Australia                    Namibia

New Mexico              Brazil                          Pakistan

 

Melody, in her book Love Is In The Earth, says of Tourmaline:  "The energy of Tourmaline relates to each of the chakras.  It acts to clear, to maintain, and to stimulate each of the energy center of the body...It is thought to bring healing powers to the user and to provide protection for all dangers occurring in the physical plane.".