Tourmaline

Tourmaline

The name was related by Christianus-Fridericus Garmann in 1707.

The name "tourmali" was a generic name used in Ceylon [Sri Lanka] for colored gemstones, usually zircons. About 1703 it had been discovered by Dutch lapidaries that some of the "zircons" that arrived in the Netherlands were in fact a previously undescribed mineral. The new mineral was given several names including "Pierre de Ceylan, by Lemery in 1717. Tourmalin, as a more or less specific mineral name, was used by Rinmann in 1766. Hill named it Tourmaline Garnet in 1771 and Richard Kirwan shortened the name to" Tourmaline " in 1794.

Data

Note to Formula: In the formula, the D-site cations are in parentheses to facilitate the assignment of the different cations among the group members to the crystallographic sites.

A = Ca, Na, K, Pb or is empty

D = Al, Fe2 +, Fe3 +, Li, Mg2 +, Mn2 +, Ti (with medium to small cations - valence balancing combinations when the A is empty)

G = Al, Cr3 +, Fe3 +, V3 + (with small cations)

Si can sometimes have a small Al and / or B3 + substitution

X = O and / or OH

Z = F, O and / or OH

Luinaite- (OH) represents a monoclinic (pseudo-rhombohedral) distorted variant (space group Cm) of the tourmaline structure. Triclinic variants have also been reported

Tourmaline includes trigonal borosillicates of the cyclosilicate superclass. The nomenclature was revised by Henry et al in 2011. The structure for the group is one in which SiO4 tetrahedra are connected into six-membered rings with a hexagonal pattern. They are stacked with intermediate deformed triangular BO3 groups and connected by cations in the D position.

The SiO4 tetrahedra are connected vertically by G site cations and X site anions, while the columns are connected horizontally by both D site cations and X site anions. The A site cations and the Z site anions occupy the channels in the center of the columns (or the A site may be empty). In addition, tetrahedral boron can be present in both natural and synthetic tourmalines (Kutzschbach et al., 2016).

Color change, from deep green to dark red, with increasing light path length, occurring in Cr-bearing tourmalines, is known as the Usambara effect. Although similar to the alexandrite effect, the color change in this case is due to (1) spectral positions of the spin allowed bands of absorption of Cr3 + ions, (2) specific ratio of the transmission of light in two transparency windows (green and red), and (3) exponential dependence of the light transmittance of the sample thickness. Chromophores other than Cr, such as Fe, suppress the effect (Taran & Naumenko, 2016).

The Tourmaline group consists of Achroiet, Buergereit, Dravite, Elbaite, Indigolite, Liddicoatite, Rubelite, Schorl, Siberite, Tsilaisite, Uvite, Verdelite and Black Tourmaline

If in stock you will find my collection of Raw Gemstones within this group below.

If you are looking for cut gemstones from the Tourmaline Group, look at TOURMALIJN GROUP