Emeralds from the Hohe Tauern (Austria): a precious stone with a long history

The mineral, emerald, represents the green variety of the hexagonal silicate mineral beryl, which has the chemical formula Be3Al2Si6O18. Its colour may be interpreted as the result of the addition of vanadium and chromium ions into the crystal lattice. In fact, the etymology of the word “emerald” is derived from Vulgar Latin, where esmeralda (f.) or esmeraldus (m.) represented a commonly spoken variant of Latin smaragdus, which itself originates from the Greek smaragdos for “green gem”.

From a historical point of view, the beginnings of emerald mining are in Ancient Egypt, where gem stones were already being unearthed in the fifthteenth century BC. The famous emerald mines located in Sikait and Sabara supplied Europe with precious minerals for more than thousand years. The gemstone was also highly sought after by the monarchs of India, Persia and the Ottoman Empire, such that it became an important merchandise. When South America fell under the domination of the Spanish crown, the European conquerors were confronted with a vivid emerald trade that ranged from Columbia to Chile and Mexico. In 1573, the Columbian Muzo mine was captured by the Spanish army and thereafter represented the most important production site in the world for emerald of gem quality.

Fig. 1. General appearance of emerald from the Central Alps. Single crystals have a size of 1 to 2cm

Nowadays, emerald is a highly esteemed gemstone achieving similar prices as equally sized diamonds. Due to the high demand, it is also produced synthetically. The process was developed by IG Farben in 1935, but satisfactory results were only achieved by Johann Lechleitner in the 1960s. Natural emerald is found in pegmatite veins and especially in gangue granites. Additionally, it occurs in metamorphic rocks and certain placer deposits (that is, accumulations of valuable minerals formed by separation by gravity during sedimentary processes). Ordinary crystals rarely exceed a few centimetres in size and are usually impaired in quality by cracks, inclusions or mineral admixtures. In general, any occurrence of emerald is associated with tectonic fault zones. Beside Columbia, Brazil and the Ural mountains in Russia, Austria, Norway, China, Afghanistan and Australia also have remarkable deposits of this gemstone. It is the Austrian emerald mines in the Habach valley (Hohe Tauern) that are the subject matter of this article.

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