Topaz
- Finder 's diamond
- Killiecrankie diamond
- Mogok Diamond
- Saxon diamond
- Slaves Diamond
The mineral topaz, also under the misleading trade names finder's diamond, Killiecrankie diamond, Mogok Diamond, Saxon diamond and slave diamond is known, is a common island silicate with the chemical composition Al 2 [( F, OH ) 2 | SiO 4 ]. The values given in the parentheses fluorine (F) and hydroxide ions (OH ) can be in the formula each represent each other (substitution, Diadochie ), but are always in the same proportions to the other components of the mineral. A F- free OH analogue is known as a synthetic compound.
Topaz crystallizes in the orthorhombic crystal system and usually develops well-educated and sometimes very large area crystals with short-to langprismatischem or säuligem habitus and glass-like sheen on the surfaces. In its pure form it is colorless and transparent. But it can also appear white and accept by foreign admixtures a yellow, pink to brownish red, purple, light blue and light green color by multiple refraction due to lattice defects or polycrystalline training, the transparency decreases accordingly.
With a Mohs hardness of 8 topaz is one of the hard minerals and serves as a reference to the to 10 ( diamond) reaching scale after Friedrich Mohs. Similar to diamond but it is however also very brittle and easy to split after the base surface (001 ) with perfectly smooth fracture surfaces, which often implies by splitting cracks in the stone. Irregular broken topazes have uneven to slightly shell-shaped fracture surfaces.
Special Features
Topaz is one of the minerals that are able to form very large and massive crystals. The largest known crystals reached a length of over a meter and a weight of up to 2.5 tons.
Before the blowpipe topaz is infusible. Topas is heated to about 1350 ° C, in the form of SiF4 fluorine escapes and moves in sillimanite and corundum. Heated with phosphorus salt, escaping hydrogen fluoride ( HF).
From pure, concentrated sulfuric acid topaz is attacked superficially, it is steeped in it decomposed. Dilute sulfuric acid will not harm topaz against it.
Etymology and history
According to the Roman naturalist Pliny the Elder, the name topaz from the island Topazos (probably St. John's Island ) comes from, which is located in the Red Sea. In fact, there was not a topaz, but olivine, mined, which was long confused with topaz. Another explanation attributes the name back to the Sanskrit word tapas, the "fire" or " lights " means.
In 1740, a topaz, the so-called Braganza Diamond, in faith, if it were a real diamond, set in the Portuguese Crown.
Classification
Already in the now outdated but still in use 8th edition of the mineral classification by Strunz was one of the topaz to mineral class of " silicates and Germanates " and then to the Department of " island silicates with tetrahedral foreign anions ( Neso - Subsilikate ) ", where he was named the " topaz group "with the system no. Formed VIII/B.02 and the other members andalusite, Boromullit, Kanonait, Krieselit, kyanite, mullite, sillimanite and Yoderit.
The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the topaz also in the department of " island silicates ( nesosilicates ) ". However, this is further divided by the crystal structure, so that the mineral according to its structure in the subsection " island silicates with additional anions; Cations iner, he " is to find where it only together with the Krieselit " and / or nurer coordination. Topaz group "with the System No. 9.AF.35 forms.
The mainly common in English-speaking classification of minerals according to Dana assigns the topaz in the class of " silicates " and then in the Department of: an " island silicates SiO4 Groups and O, OH, F, and H2O". Here he is as the namesake of the " Topaz group " with the system no. ": With cations SiO4 Groups and O, OH, F, and H2O only in coordination island silicates " to find 52.03.01 and the other Member Krieselit within the subdivision of.
Modifications and varieties
A well-known variety is Pyknit, a straw- yellow, yellowish - reddish or greyish-white, stalky grown topaz aggregate.
Education and Locations
Topaz is found prismatic in shape, on the base had grown up crystals, but in addition also solid or in a granular variant. He usually occurs together with beryl, tourmaline and apatite minerals of in acidic igneous rocks such as granite -associated pegmatites, next he comes in gneisses and as a mineral soap, for example, in river sediments. In Brazil, there are large deposits in which particularly large crystals were found.
Historically particularly significant was the occurrence wine yellow crystals in Schneckenstein in Vogtland: thence come the ground topaz jewelery by August the Strong (now in the Green Vault in Dresden) and in the English crown. Another significant topazes was the great Moghuls: 157 1/4 ct.
Other localities include Badakhshan, Laghman and Nangarhar in Afghanistan; Tamanrasset in Algeria; the region around Mandalay in Myanmar ( Burma Burma engl. ); the island of Honshu in Japan; several regions in Mexico, Norway, Pakistan and Sweden; the Damphreux and other regions of Switzerland; the Central Province and Sabaragamuwa in Sri Lanka; the Czech Republic; and many regions in the United States. Also in the eastern region of Antarctica topazes have been found.
Topaz crystals can be very large in favorable formation conditions. Crystals of 100 kg or more are not uncommon. The largest topaz crystal ever found to have a length of one meter and a weight of 2,500 kg, and have been found at Ribáuè, Alto Ligonha in Mozambique. In Smithsonian Institution two uncut crystals of 31.8 kg ( " Lindsay Topaz" ) and 50 kg ( " Freeman Topaz" ) to be issued, which are also among the largest in the world.
Crystal structure
Topaz crystallizes in the orthorhombic space group Pbnm ( Raumgruppen-Nr. 62) with the lattice parameters a = 4.65 Å; b = 8.80 Å and c = 8.39 Å and four formula units per unit cell.
Use as a gemstone
Topaz is a precious gemstone that is not overly expensive, however, due to its relative abundance, even with large and high quality pieces. Exception is in nature very rarely occurring blue topaz, which is also referred to as " precious topaz " and also rare, orange-red " Imperial Topaz " or "King topaz ".
Due to its perfect cleavage after the basic surface Topaz is a difficult stone to be processed. Quick temperature changes and carelessly conducted barrel work can already lead to cracks and fissures in the stone. Also it does not tolerate an ultrasonic bath, if it has many pockets.
Manipulation and imitation
Many topazes are changed in color by treatment. This can occur by irradiation with gamma rays or electron beams ( blue) " Idar- Blue" ( brown, greenish brown) or by heating (blue, red ) happen. This is how, for example, the dark green, brown or purple Mystic Fire Topaz (trade name) or the Indian -Summer- Topaz ( trade name), pink to light purple. Even retailers such as Tiffany & Co. put an irradiated and heated Topaze.
Despite their name, Madeira and smoky topaz not real topaz minerals. The first one is a trade name for Citrine yellow or burnt amethyst, the latter is a smoky quartz. All are with the genuine topaz in no way related minerals, but macrocrystalline quartz varieties.