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Feldspar - Feldspat - Feldspath - Feldespato Europe : Germany : Potassium - Feldspar crystals up to 1 m at Zwiesel - Rabenstein Coordinates : 49°03'N , 13°10'E : Quarzbruch Hennenkobel (Hühnerkobel), Kiesau, Rabenstein, Zwiesel, Bavarian Forest, Bavaria, Germany For a detailed hiking map of this locality please click here

Agreed : The feldspar crystals at the Quarzbruch Hühnerkobel are not the largest in the world, but they are easily the largest feldspars still accessible in Middle Europe. And the locality as such is one of the most classic one both in mineralogy and petrography. More than 40 different phosphate minerals have been found here by mineralogists and collectors. And among the famous mineral localities of Germany : St. Andreasberg, Neudorf, Freiberg, Ilfeld and Bad Ems, the Hühnerkobel definitely is one of the best known. But be aware : It is not that easy to find this locality. In the very beginnings of my mineral collecting career - way back in the 1970ies - I spent a beautiful holiday in this area with my father. We searched for minerals at a lot of different places and we found many interesting specimen, at least for the beginner I was at that time. But we couldnt find the famous "Hühnerkobel" pegmatite on any map. We even asked some locals in the nearby town of Zwiesel - sometimes pretty hard to understand due to their very bavarian accent - but nobody was able to help us. In fact it took 25 more years, before I finally managed to visit the Hühnerkobel Quarzbruch. Just some weeks ago. Click here for the weather conditions. The reason why we were not able to locate this locality is fairly simple. The 'Hühnerkobel' does not exist in modern language. It is a sort of fictional mineral locality, which only exists in many publications and of course in the minds of countless mineralogists and collectors. But in nature there is no such place as the 'Hühnerkobel' It is known to every local as Hennenkobel and this is also the name printed on the maps! So if you ask for the 'Hühnerkobel' you will only earn funny looks and long faces... The quarry at the Hennenkobel went in operation in 1756, when a Mr. Wissger started quarrying quartz for the florishing glas industry in the Bavarian Forest. The open pit was exhausted in 1831 and underground mining took place until 1877, when the whole operation was abandoned. Later attempts to extract the remaining feldspar proved unsucessful. However, though large scale exploitation ended in 1877, small scale operations to exploit rare minerals have never stopped since. Over the years more than 70 minerals, many of them rare phosphates, have been described from this single pegmatite body. Among them are Phosphoferrite, Triphylite, Xanthoxenite and Zwieselite, for which the Hennenkobel is the type locality. Today the 'Quarzbruch' is part of the Kiesau Nature Reserve and though the quarry is basically open to the public, collecting is reserved for scientists only. The quarry walls nicely display the zoning of the pegmatite body, but the most spectacular part of it - the underground portion with the large and well developed feldspar crystals - is still unacessible. Though there is hope, as the community of Zwiesel plans the opening of the "Underground Lake" to the public, which will certainly draw a lot of more tourists to the site.   The Hennenkobel Quarry in a nutshell : Mineralogy : Potassium - feldspar crystals within quartz - mica matrix with some minor (but famous) phosphate minerals Crystal Size : 1 m large crystals are visible in the walls of the 'underground lake' confirmed Geology & Origin : pegmatitic Current status : The old open pit is freely acessible, but do not exhibit particular large crystals. The partly drowned underground workings with the large feldspar crystals are gated, but a more favourable presentation is in the planning. Remarks : This will be a spectacular geosite as soon as the old underground workings are open to the public   Other notable & famous feldspar occurences : Note : Strictly speaking, the term "Feldspar" refers to a large group of tectosilicates such as Albite, Anorthite, Orthoclase and some others. For more information about the more common members of the feldspar group please click here. Members of the feldspar group may be (apart from quartz possibly) the minerals with the largest crystals in existence. There are several rumours around about sizeable quarries in a single feldspar crystal. An example is the Devils Hole mine, Colorado, where a crystal of the size 50 x 36 x 13 m is reported from. However it is difficult to verify those rumours, even on site, as it is not easy to determine accurately the true extent of a single crystal that large. Feldspar crystals of one meter and more are a common constituent of pegmatites worldwide and too many to name here. In fact, pegmatites are defined by the gigantism of its minerals, of which members of the feldspar group are among the most common ones. These feldspar crystals usually Do NOT exhibit any freely developed crystal planes, but rather form giant crystalline "feldspar - grains" swimming inmidth of other feldspar (quartz, mica etc.) grains. There are however many noteworthy occurences of freely developed feldspar crystals, which may reach considerable sizes : - Excellent tabular cleavelandite ( = variety of albite ) clusters up to 15 x 10 cm occur in large cavities in the Rutherford Mine, Virginia and in the Pikes Peak massive, Colorado. Other spectacular cleavelandite crystal "books" are known from the tourmaline pegmatites of Pala and Hercules mine, California. - Pericline, another variety of albite, is known as a major constituent of hydrothermal alpine fissure mineralization. Many alpine localities with excellent specimen are known, whereas the largest reported pericline crystals, reaching almost 20 cm - came from Gibelmatte in the Binntal, Switzerland. - Exceptional well crystallized orthoclase crystals are known from many granite pegmatites such as Strzegom / Striegau in Poland and from Baveno in Italy. Another renowned locality are the alkaline pegmatites of Mt. Malosa, Zombas, Malawi, where excellent orthoclase crystals may reach 20 cm and more and often form perfect "Karlsbader" twins. - Gemmy yellow Orthoclase crystals of up to 10 cm are known from a small locality at Itrongay, Madagascar - Splendid green amazonite crystals, a variety of the microcline feldspar, up to 40 cm and more are known to occur at various localites such as Pikes Peak, Colorado and recently from Konso, Sidamo Province, Ethiopia.

Old quartz quarry at the Hennenkobel, famous for its phosphate paragenesis Photo : Giant Crystal Project   Large yellowish potassium - feldspar crystals in quartz - mica matrix Photo : Verein 'Unterirdisches Zwiesel e.V.   Another romantic view of the large feldspar crystals Photo : Verein 'Unterirdisches Zwiesel e.V.     Resources and relevant weblinks : For more information on this famous mineral locality please look at www.mindat.org There are some scattered older publications about the Hühnerkobel / Hennenkobel locality, namely in the "AUFSCHLUSS" - the mineral magazin of the german VFMG = Verein der Freunde der Mineralogie und Geologie. The best recent publication is probably : PFAFFL, F. (1981) : Die Mineralien des Hühnerkobel Pegmatites bei Zwiesel; pp. 36 - 50 in : PFAFFL, F. (1981) : Die Mineralien des Bayrischen Waldes, Morsak Verlag 1981 The best online publication available is of F. Wrobel in german language and can be found here. If you want to explore some 3D - panoramic images of the locality, please click here.