What are the least known minerals

Mendig

Preface

At the beginning of 1973, the gemstone cutter Philip Hobein from Kirschweiler near Idar Oberstein discovered some blue grains of crystalline formation behind the restaurant 'Laacher Mühle'. These grains aroused his interest, especially since he already had some experience in cutting various minerals that are not known as gemstones. In his workshop, he provided these xenomorphic grains with a facet cut. The result was the birth of a new gemstone of sapphire blue color and very beautiful transparency - the mineral Haüyn, named after the French crystallographer R. J. Haüy (1743 to 1822) (Brunn-Neergard, 1807).

The comprehensive data on this rare cubic framework silicate of the sodalite group according to the STRUNZ system can be found in the mineral profile from the user lexicon under Haüyn.

location

Two quarries are located near the Hansa Hotel, on well-signposted paths in the direction Wingertsbergwand, about 20 minutes, past the outdoor pool. The quarry owned by H.W. Schmitz am Wingertsberg consists primarily of basalt lavas with pumice layers. The Wingertsbergwand is testimony to the most powerful volcanic eruption in Central Europe 13,000 years ago, the Eruption of the Laacher See volcano. On this wall, which is up to 50 meters high, you can see the different layers of ash from the various eruption phases.

In the quarry In the dents (now: 'Grube Zieglowski'), according to literature and according to information from some collectors, there are the world's best Haüyne in almost all shades of blue and sizes up to the exceptional case of the facettable 5-carat.

The best place to begin an exploration of the volcanic world around Lake Laacher See is in private German volcano museum (Brauerstr. 5, 56743 Mendig). In the brewhouse of a former brewery there is a rather extensive one Mineral collection which gives an overview of the broad spectrum of volcanic science.


Mendiger Eifel volcanism

From a geological point of view, volcanism in the Eastern Eifel is still very young. It was 'only' 13,000 years ago that the largest volcanic eruption in Central Europe occurred. At that time the huge caldera of the Laacher See was created. With an eruption column 40km high, the volcanic eruption terrified the people living in the area at the time. Pumice and basalt lava have been deposited meters thick in a wide area. The Laacher See owes its existence to an underground collapse Magma chamberwhich, however, is far from being emptied. Seismological measurements have shown that there is still a magma-filled cavity under the lake at a depth of 3 km. As a volcanic greeting, carbon dioxide bubbles out of the earth's interior on the eastern shore of the lake. The volcanologists also believe that the Eifel volcanoes have not gone out, but are only asleep. The youngest Eifel volcano, the Ulmener Maar, was only formed 10,000 years ago. The Bochum-based volcanologist Hans-Ulrich Schmincke thinks "that many eruptions can be expected in the very near future". How soon - but the experts cannot predict that.

Mendig lies in the middle of the cooled lava flow of the Wingertsberg volcano, which covered the land with magma and ash 200,000 years ago. If you want to go into the middle of such a flow of cooled magma, you only need to descend 150 steps at the volcano museum into the 32 meter deep underworld to the largest basalt lava plant in the world. The whole of Mendig is undermined because the valuable lava rock has been brought to light by miners for centuries. The vesicular or porous stone was processed into slabs, building stones and mill stones as well as raw material for sculptors. Many Mendig houses still show the gray-black lava look today. The lava has solidified in mighty hexagonal columns (see> Basalt column).

In order to hold the overburden, the miners left some of these pillars. Spacious caves were created, for which a completely different purpose was soon discovered. Since there were no cooling machines in the last century, the beer quickly went bad in the summer. Only in Mendig was there good beer even in the hottest summer. And why was that so? Quite simply: The Moravian Brotherhood, a Protestant religious community, was the first to use the Mendig lava caves as a rock cellar to store beer at the constant temperature of 6 ° C. In 1842 the Moravians even built an underground brewery in the lava vaults. After all, a total of 28 breweries worked in Mendig in the past century. The beer caves are not accessible in winter, as they then serve as resting quarters for the largest bat colony in Rhineland-Palatinate.

In the lava caves there is 72% humidity at a constant 6-9 ° C. The admission price for this tour without a visit to the Wingertsbergwand and without a tour of the Mendiger Museums-Lay is € 3.50 per adult.

The Mendiger Museum Lay is an open-air exhibition just a few steps away from the volcano museum. At the entrance there is an old working mine railway, in the background there is a slewing crane like the one used in the open pit. There is also a stonemason's hut and a blacksmith's shop. Numerous tools give an idea of ​​how paving stones and millstones are worked. The "very rich" sculptor Werner Geilen has his studio here and chisels excellent figures out of the stone.


Find report, explanations and experiences

from Ralf

Search for minerals in the ejecta in the area around the Laacher See

I have been collecting in the Laacher See area for many years now, primarily "In den Dellen". If you come to the sieve pile, you will often find open and abandoned ejections, in which the "knocker" probably did not suspect anything interesting. Here I would like to briefly describe what you should pay attention to when collecting there, or which ejections are interesting. The experienced Eifel collectors know that for sure, but maybe one or the other can do something with it.

The inexperienced collector looks for ejecta with holes. Because, so the logic says, minerals can only crystallize freely where there is a cavity, that's true. As a result, ejections that appear tight from the outside are often knocked open on the spot and left because there are no recognizable cavities. But there is actually no ejecta that is completely sealed. After that, there is almost no ejecta that is free of minerals. The minerals are often very small and can hardly be seen with the naked eye or with a magnifying glass. The vast majority of rare minerals do not form in the bladder cavities, but in the interstices of the sanidine crystals. For example, baddeleyite, which is described as rare, is just as common as zircon. In most cases, however, it is simply overlooked. A baddeleyit <0.5mm is mostly overlooked outside with a 20x magnifying glass.

Here is an overview of the most disdained ejections and what you can find in them

Crumbly, white to gray ejections, often streaked with small "rust spots" on the edge (approx. 5-10cm in size), you can crumble between your fingers. These ejections can include z. B. Baddeleyit, Zirconolite, Fergusonit and Calciobetafit contain. The extremely rare fersmit also appears in it. Look out for dark red pyrochlores and tiny black magnetites. Both can be fatally incorrect. Dark red pyrochlores are sometimes calciobetafite and the black magnetites can be aeschynite. The latter can be clearly recognized by the crystal shape, but you often don't look too closely and categorize small and black as magnetite. Often there are no holes at all in these ejections. The minerals sit in the small spandrels of the sanidine crystals that make up these ejecta. They look dense even from a distance of 20 centimeters. Due to the high whiteness, these gussets cannot be recognized. In addition, you should pay particular attention to the edge area. The minerals are often only an inch or two below the crust, while nothing can be found inside.

Coarsely crystalline ejections, often appearing completely or partially melted and with a gray, blistered appearance. Often interspersed with black, oily streaks, they usually contain fused pyroxene, titanite and colorless to pale blue skin. But that doesn't matter. Here you can find corundum, hercynite and ilmenorutil. Interestingly, these are mostly not, or only very slightly, merged. Also contained therein, but not together with the aforementioned, can be bustamite, ferrosilite, forsterite and tephroite.

Ejections appearing very dense with clearly visible, coarse calcite. Cavities mostly glassy and lined with green glass are almost always of no interest. But I found my largest Låvenit (1cm) in it. Secondary aragonite is very often found in the form of tufts or hedgehogs. Calcite is very interesting for UV freaks because it can fluoresce deep red. If he does that and there are magnetite crystals in it, they should be analyzed. The fluorescence indicates a higher manganese content, which in turn is an indication of Jacobite. Unfortunately, magnetite and jacobsite cannot be distinguished optically. In four out of five cases it is really just magnetite or a mixed crystal magnetite-jacobsite.

White, coarsely crystalline ejecta which are still surrounded by blistered lava at the edge. Pure white and mostly without any further mineralization. Look closely and if there is something in it that is not white, be sure to take it with you. In it I found, unfortunately only once, euxenite-polyclass mixed crystals and ilmenite. Often also pyrochlore, sometimes in tabular form or even as a rosette.

Gray, bone-hard ejecta look like lava from the outside, but are smooth and have light gray, elongated spots 1-2mm in size. Because of their hardness and their appearance, we call them "betonite" for fun. Most of them are not even tapped, but they have their own, highly interesting paragenesis. You can also confidently open it in the break and look for cavities. There are no crystal gussets and you can leave them lying around without cavities. Here you can find: dolomite, hedenbergite, britholite, zircon in pagoda-shaped crystals, muscovite, quartz crystals and, as an individual find, fergusonite.

Light brownish, sandy-looking ejectawhich are very similar to the typical, zirconium-containing ejecta, but contain no bladder cavities, only crystal gussets. These are typical fergusonite suspects. Usually there are also small titanites and zircons, which are hardly worth collecting. They are seldom completely interspersed with fergusonite. My best eject was about the size of a football and had over 500 Fergusonites in one half. I gave up the other half because I didn't feel like formatting anymore. Usually, however, there are only a few crystals in it, also here preferably in the edge area.

Black, hard and heavy ejections almost look like lumps of tar. Only rarely do they have cavities in which one then believes to see masses of pyroxe crystals. The whole ejecta consists almost of this material. But it is actually actinolite.

Light gray ejections, sometimes very hard, sometimes soft, are somehow reminiscent of rounded basalt lumps. If you open them, you sometimes see cavities that are lined with reddish-brown glassy material. These sometimes contain magnesite, dolomite or siderite; very rare nepheline, but that in beautiful clear, flat-sheet crystals.

"Lumps of rust": they really look like a piece of totally rusted iron. Are often very tough. If you open them, they are black and oily shimmering on the inside. If they have cavities, you can often find light yellow to orange-colored, crusty deposits in them. This is jarosite (orange) or alunite (light yellow). Only analysis allows a reliable determination. Jarosite very seldom forms beautiful tabular crystals, but they are always very small. Furthermore, you can sometimes find wonderful gypsum crystals up to 3mm in size. Rozenite can also occur, but can only be reliably determined by analysis.

Ejections containing fluorite: Hardly anyone leaves them lying around, because they usually have clearly visible cavities, which are usually highlighted in gray and black. In addition to spherical fluorite, it often also contains Wöhlerite and Lavenite. I do not mention it because of that, but because of one of the most frequently misidentified minerals in the Laacher See area, the idzenite. Götzenit is found in ruler-like, flat-paneled crystals that always have a beveled end face. They are whitish to transparent and have a silky shimmer. The most important thing, however, is that idolite cannot be determined optically and is extremely rare. I claim that 95% of all unanalyzed idols in all collections are none. There are such latte, white to colorless, sometimes yellowish crystals in many ejections. However, these minerals are usually amorphous. Of more than 50 samples from a first series, we were only able to detect flawless idolite four times. Always in paragenesis with fluorite, wöhlerite and lavenite. And always in the ejections whose cavities were highlighted gray-black. From these we later analyzed 20 samples again and only found 6 idols. So, idol can never be determined optically or on the basis of paragenesis!

With these explanations I do not claim to be exhaustive in any way. There are still a lot of different ejecta and minerals to be found there and of course there are also many that do not contain anything interesting. It has only been important to me for a long time to let the less experienced collectors know what they might leave behind. I think that I know my way around the subject very well and with increasing experience I have learned to assess the ejections. The sum total of this experience led me to the fact that today I know that I know nothing (stolen, I know). That means the hammer is only there to scratch. Basically, no ejecta is opened in the break, but always taken. Only at home with the crackle and the stereo microscope do you look inside. Each piece is cracked at least four times, once always along the edge. The cracked pieces are always kept separate until the last piece is examined. Only then do they go to the scrap in the bucket. Sometimes it is precisely this last piece that shows an interesting mineral. And you shouldn't believe how similar cracked ejections are in a big bucket when you try to find the remaining chunks of this ejecta. Oh yes, again for the baddeleyit. This is the work of the devil. Maybe I have a strange look in this regard, but I almost always didn't find the baddeleyite until I saw zirconolite. These little red needles are easy to see under the steromicroscope. Only when I looked very closely and with great concentration did they suddenly appear, the Baddeleyite.