Prehnite
Prehnite, outdated also known as Aedelit, Chiltonit, Coupholit and Edelit or under the trade names Cape and Cape beryl Emerald, is a commonly occurring mineral from the mineral class of " Silicate and germanate ". It crystallizes in the orthorhombic crystal system with the chemical composition Ca2Al [( OH) 2 | AlSi3O10 ] and developed mostly tabular to prismatic crystals, also foliated, fan-shaped or grape-like to spherical mineral aggregates of white, gray or yellowish to greenish color. Even colorless Prehnite Prehnite and cat's eyes are known.
Special Features
Prehnitzwillinge according to (100) are pyroelectric toward the a-axis. Before the blowpipe Prehnite melts easily and flakes or puffs up here. Only at high temperature also water forms.
Prehnite is relatively insensitive to acids and is completely destroyed by them only after the annealing, but is very sensitive even to small heat affected.
Occasionally shows Prehnite with short wavelength UV light blue white or peach colored and yellow with long wave UV light fluorescence.
Etymology and history
Prehnite is one of the first minerals, which is named after a person. The Dutch Baron and Colonel Hendrik von Prehn (1733-1785) brought some 1783 samples from the Cape Province ( Cape of Good Hope ) with and let them analyze by Abraham Gottlob Werner. He recognized the material as a new mineral and named it after his page.
As exact type locality is now the dolerite deposits of Karoo near Cradock in the Eastern Cape of South Africa.
Classification
In the now outdated 8th edition of the mineral classification by Strunz the prehnite is part of the Department of " silicates and Germanates with transitional structures between chain and layer silicates ", where it forms a separate group with Amstallit, Bavenit, Chiavennit, Rudenkoit and Tvedalit.
Since the extensively revised 9th edition of the Strunz'schen Mineral classification class of silicates is partially re-defined and precise subdivided according to the structural design and the prehnite now finds itself accordingly in the subdivision of " transition structures: Chain and chain silicates - layer silicates ", where he is the unnamed group 9.DP.20 the only member.
The commonly used in English-speaking classification of minerals according to Dana sorted the prehnite also in the class of silicates, there, however, in the department of " layer silicates: Two-dimensional infinite layers with other than six -membered rings: 4 - membered rings ", where he also is the only member the unnamed group forms 72.1.3.
Education and Locations
Prehnite occurs either secondarily of other minerals or by hydrothermal processes in clefts, corridors and geodes within igneous or metamorphic rocks (eg, gabbro, diabase, melaphyre, crystalline schist). Prehnite is often found in paragenesis with Apophyllite, Calcite, Datolith, epidote, native copper, Pectolite and various zeolites. In addition, it forms pseudomorphs after analcime, among other things, Naumontit and Natrolite.
Worldwide Prehnite has been (as of 2011) detected at about 1,400 localities. In Germany was the mineral, especially in Bavaria, more precisely in the Black Forest, the Fichtelgebirge, Spessart, Bavarian Forest, in Swabia and the Upper Palatinate; in Hesse Lahn- Dill-Kreis and Odenwald; in the Harz (Lower Saxony, Saxony- Anhalt); Sauerland (North Rhine -Westphalia); in Rhineland-Palatinate Hunsrück, low churches and Wolfenstein; in the Ore Mountains and the Upper Lusatia in Saxony; in Elmshorn and Lübeck in Schleswig -Holstein and in the Thuringian Forest and Wurzbach.
In Austria, prehnite found in many regions of Carinthia, Lower Austria, Salzburg, Styria, Tyrol, Upper Austria and Vorarlberg. In Switzerland, prehnite was found in several regions of the cantons of Graubünden, Ticino, Uri and Wallis.
Other localities are Egypt, Antarctica, Argentina, many regions in Australia, Belgium, Bolivia, Brazil, Bulgaria, Chile, China, Costa Rica, Ecuador, Finland, several regions in France, Greece, Greenland, India, Indonesia, Ireland, Iceland, Israel, many regions in Italy, Japan, several regions of Canada, the Channel Islands, Kazakhstan, Kenya, Colombia, Croatia, Madagascar, Mali, Morocco, Mexico, Mongolia, Namibia, New Zealand, North Korea, many regions in Norway, Oman, Pakistan, Papua New Guinea, Peru, Philippines, Poland, Portugal, Reunion, some regions in Russia, several regions in Sweden, Slovakia, some regions in Spain, several regions in South Africa, South Korea, Tanzania, Trinidad and Tobago, more Bohemian and Moravian regions in Czech Republic, Turkey, Ukraine, Hungary, the United States Virgin Islands ( U.S. Virgin Islands ), many regions of the United Kingdom ( UK) and many regions in the United States of America (USA).
Also in Gesteinsprobem the Mid-Atlantic Ridge, more precisely, the " Markov - depth" within the Sierra Leone Fracture Zone and the Indian Ocean, more precisely the central Indian ridge could be detected prehnite.
Crystal structure
Prehnite crystallizes in the orthorhombic space group P2CM with the lattice parameters a = 4.65 Å; b = 5.48 Å and c = 18.49 Å and two formula units per unit cell.
Use as a gemstone
So far, prehnite is exclusively, though not very often processed into semi-precious stones and offered depending on the quality in different types of grinding and shapes. Due to color similarity confusion among others, apatite, brazilianite, chrysoprase, jade, peridot, periclase and serpentine.