05-14 Tourmaline

05-14. Tourmaline – Elbaite #1.

Week 2 of this short exploration of the tourmaline geometry. The Elbaite has a similar geometry structure than the Dravite but its chemical composition is different. It should make for interesting compositions in terms of color and density of shapes.

Elbaite comes in virtually every color of the spectrum and has unique optical properties. Many green and blue specimens are strongly pleochroic. When viewed through their vertical axis, they appear darker in color than when seen through their horizontal axis. Certain Elbaites exhibit a cat’s eye effect when polished.

Brazil, Afghanistan, Italy are some of the countries where some of the most beautiful minerals were found. 

Dutch traders brought tourmaline to Europe in the 1700s. They gave it the name, Aschentrekker, or “ash puller,” because they used the crystals to pull ashes from their Meerschaum pipes. This ability to gain magnetic powers and become electrically “polar” by means of heat distinguishes Tourmaline from most other gems. It is doubtful this custom is still practiced today considering the value of the gems!

From a resource by Bosi, Andreozzi, Federico, Graziani, Lucchesi: crystal chemistry of the elbaite-schorl series, Minas Gerais, Brazil.

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04-02

04-02. Topaz #1.

Topaz is the mineral of week #14 in this 52 weeks tour of Geometry of Nature. The topaz crystal belongs to the orthorhombic system – three unequal axes at right angles resulting in a rectangular prism with a rectangular base.  It is very hard but easy to break. Pure topaz is colorless and transparent but, depending on the inclusions, it is often found in a wide range of color brown, blue, green, yellow, orange, red, pink, and purple.

The most important Topaz deposits are in Brazil. The famous golden orange-brown Imperial Topaz come from the famous occurrence in Minas Gerais at Ouero Prito. Multicolored yellow and blue Topaz comes from Russia. Classic yellow Topaz crystals come from Germany.

Legend has it that Hildegarde of Flanders, wife of Theodoric Count of Holland, presented a topaz to a monastery in the town of Ghent. It emitted a light so bright at night that prayers could be read without the aid of candles in the chapel where it was kept.

04-02