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.
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.
The Habach valley – home of the greatest emerald mine in Europe
The Habach valley is a side valley of the Salzach valley in the Central Alps of Salzburg in Austria. The entrance to the emerald mine is located in the middle of the valley at the so-called “Söllgraben” at an altitude of 2,200m (Fig. 1). The landscape is highly susceptible to rockfalls, so any expedition to the mine bears certain risks. Close to the mine is a small house (“Berghaus”) offering shelter for tourists and mine workers. From a geological point of view, the emerald mine is situated in a lithology mainly consisting of fibrous and banded gneisses, as well as serpentine-talc schists. In these rocks, high numbers of pegmatite gangues are embedded, which bear increased amounts of beryllium and therefore offer the ideal preconditions for emerald growth. The chromium required for the green colour of the mineral is primarily depleated from the adjacent serpentine rocks.
The origin of emerald mining in the Habach valley probably dates back to the Bronze Age, when the original inhabitants began to extract the “green gold”. It is commonly believed that mining activity was continued by the Romans. According to a legend, the Roman emperor Nero possessed an emerald from the Habach valley, which was ground to a monocle to improve his visual acuity. Unfortunately, any evidence for the use of the mine during the Middle Ages is missing, although several scientists think that the 51.5 carat emerald decorating the crown of the French monarch Louis IX (1226 – 1270) came from the Habach valley.
In the seventeeth century, emerald was subjected to systematic mining in the valley, including the establishment of the necessary infrastructure. At the beginning, the profitability of the emerald deposit was very low and therefore the economic exploitation of the mine was not crowned with great success. This was mainly due to the fact that the mine is situated on a high-alpine altitude level and is therefore very difficult to access. In 1669, the Florentine aristocrat, Anna of Medici, engaged the famous geologist, Nils Stensen, to evaluate the productiveness of the emerald mine in the Habach valley. About 130 years later, first detailed descriptions of the emerald deposit were provided, in which the name “Heubach” valley was used instead of Habach valley. Further geological and mineralogical descriptions of the mining area date back to the nineteenth century, after the earth science of the area had been well established within the scientific community.
In the middle of the nineteenth century, the Viennese jeweller, Samuel Goldschmidt, purchased the mine and ordered the construction of a shelter (the Berghaus referred to above). Furthermore, three tunnels were driven into the rock to increase the productivity of the mine. From that period also dates the most precious emerald ever found in the Habach valley, namely a 42 carat gemstone, which is stored together with the crown jewels in the Tower of London. At the end of the nineteenth century, a fourth tunnel was driven into gneisses and serpentine rocks and, from 1896,the business came under the management of Esmerald Mines Ltd established in London. Within a period of about 17 years, the company reached an output of 32,000 carats of impure emeralds and 7,000 carats of pure emeralds possessing gem quality (Fig. 2).
In 1913, the mining process had ceased due to debts of the managerof the company. This situation was taken advantage of by a consortium led bythe local government in Bramberg, which purchased the whole mining area for arelatively small amount of money. Only four years later, the the German entrepreneur, Anton Hager, owner of a saw mill in Traunstein, came into possession of the mine. After ten years, the mine again changed owner, because the rent it could achieve was much too low. After World War II, Hans Zieger, a former colonel of the Wehrmacht, became managerof the mine and worked there for four years. In the 1960s, the mine came into possession of Karl Gaab, who leased the production to a number of different people. Since the beginning of the 1990s, the Steiner family has acted as leaseholder of the mine and has been rather successful in the management of this small company.
The emerald mine and tourism
Since the 1990s, the Habach valley has attracted lots of casual and professional mineral collectors. From a tourist point of view, the local gemstone deposit is advertised in Austria and the whole of Europe. Therefore, the village Bramberg has been renamed the “Emerald Village of Bramberg” and a new hotel serving as base camp for the collectors has been built at the valley entrance. Although professional mining activity is limited to a few specialists, in the meantime, lots of small emeralds canalsostill be found in the sediments transported in the river Leckbach. The gemstones are separated from the gravel and sand by using pans that are also usedto prospect for gold.
Modern tourist attractions include a special emerald trail, leading to the locations of historic gemstone mining, and workshops where interested people learn the techniques of panning for minerals. With a little patience and luck, finds of small emerald crystals are definitely possible and these may havea remarkable value for the collector due to their rareness. Currently, the yearly tourist period in the Habach valley lasts from late spring to autumn.
Typical appearance of the emeralds
Emerald originating from the Habach valley is characterised by a pronounced green colour, which may be the result of both the high chromium content in the mineral and the dark colour of the host rock. Like other emeralds from all over the world, it develops hexagonal prims with the highest cleavage occurring perpendicular to the main crystallographic axis. Emerald from the Habach valley has the lowest number of crystal faces among all emeralds worldwide and exhibits characteristic indentations in the faces of the prims and a tabular appearance (Fig. 3).
Flawless emerald crystals are found very rarely in the Habach valley. Most minerals are characterised by one or more inclusions, which makes it difficult to give them a gemstone cut. However, scientific investigations have yielded evidence that emerald crystals from the Hohe Tauern may bear up to fortyspecies of mineral inclusions, among which phenakite, a beryllium orthosilicate, and biotite play a major role. If the provenance of an emerald is not known, microscopy of its inclusion phases canhelp to find a geographic classification of the gemstone.
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