Emeralds are rare
|Emerald - rough stone|
|Chemism||Al2Be3[Si6O18], Addition of Cr3+ and V ions|
|Mineral grade|| Ring silicates (cyclosilicates)|
see beryl (after Strunz)
|colour||dark to light green|
|Mohs hardness||7.5 to 8|
|Density (g / cm³)||2.6 to 2.8|
|transparency||transparent to translucent|
|Frequent crystal faces|
|Refractive index||ω = 1.568-1.602 ε = 1.564-1.595|
|Δ = 0.004-, 0.007; uniaxial negative|
|Pleochroism||natural: green-blue-blue-green to yellow-green; synthetic: yellow-green-blue-green|
| Angle / dispersion|
of the optical axes
|Similar minerals||Demantoid, Diopside, Dioptas, Grossular, Green Tourmaline|
|Special marks||many inclusions and cracks|
emerald is a variety of the silicate mineral beryl which crystallizes in the hexagonal crystal system and has a hardness of 7.5 to 8. Its chemical composition is due to Be3Al2Si6O18 described. The color is green due to the admixture of chromium and vanadium ions, the line color is white.
Etymology and history
The word "emerald" was derived from the Latin. emeraldus from the Greek σμάραγδος, smáragdos borrowed and is with Sanskrit marakatam related; however, the word is probably of Semitic origin, see akkad. barraqtu "Shiny stone", to the root BRQ "Shine" and Hebrew ברקת (bāreqet), "Emerald" to ברק (bâraq), "Flash".
Emerald mining began in ancient Egypt. As early as the 13th century BC The gemstones were mined there; the mines of Sikait and Sabara supplied Europe with the precious minerals for more than a thousand years. The precious stones were also in great demand in the Orient with the Persians, Ottomans and the Mughal rulers of India. When the Spaniards finally conquered South America in the 16th century, they also encountered a brisk trade in stones there, which reached from Colombia as far as Chile and Mexico. The Muzo mine, captured by them in 1573, replaced the Egyptian sources from then on.
In 1935 I.G. Colors in Bitterfeld were the first to produce synthetic emeralds in grindable quality. They were used for advertising purposes under the name Igmerald, a made-up word I.G. and the English word emerald for emerald, expelled.
- Trapiche emerald - rare crystal formation in the form of a wagon wheel with spokes from Colombia (no twin)
- Emerald cat's eye - with a cat's eye effect
Education and Locations
Emeralds are found in pegmatite veins, especially in granites, but also in metamorphic rocks such as gneiss and as mineral soap in river sediments. The crystals are rarely larger than a few centimeters and their quality is usually impaired by cracks, inclusions (often biotite and other mica or liquids) and admixtures of other minerals. Their occurrence is linked to tectonic fault zones. It is possible to make emeralds synthetically.
Important deposits can be found in Colombia, Brazil and the Ural Mountains. Smaller occurrences can be found in southern Africa. The only relevant sites in Europe are in the Habach Valley in Austria and Norway.
The largest emerald weighs 16,300 carats and is in the Topkapi Seraglio Museum in Istanbul.
Use as a gem stone
Emeralds were and are valued by many cultures around the world as particularly valuable jewelery and precious stones. The emeralds from Brazil in particular can achieve higher prices than a diamond of the same size due to their strong green.
The emerald deposit is an economic factor that should not be underestimated. All countries export most of the stones. In Colombia, emeralds are exported annually with an official trade volume of between 150 and 400 million US dollars, with the same amount having to be added for the black market.
Manipulations and imitations
In terms of its optical properties (color, luster), emerald is very insensitive, it only changes color at around 700 to 800 ° C, but it often shows an uneven color distribution and, due to many cracks and inclusions, clouding of color and sensitivity to pressure. This is counteracted in the jewelry industry by using uncolored synthetic resins, for example, to protect the stone stabilized or colored oils and resins colored becomes.
As one of the most valuable and correspondingly expensive gemstones, the emerald range is often supplemented by syntheses and imitations. Minerals similar in color, such as green-colored minerals from the tourmaline group, Dioptas and the garnet varieties Dematoid and Grossular are used as well as colored glass.
- Edition Dörfler: Minerals encyclopedia, Nebel Verlag, ISBN 3-89555-076-0
- Prof. Dr. Martin Okrusch, Prof. Dr. Siegfried Matthes: mineralogy, Springer Verlag Berlin (2005), ISBN 3-540-23812-3
- Prof. Dr. Walter Schumann: Precious and semi-precious stones, BLV Verlags GmbH Munich (11th edition), ISBN 3-405-15808-7
Categories: Gemstone | Variety (mineralogy) | Hexagonal crystal system
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