2001, Fluorite from the Summit Cleft, Weisseck

 

 

Weisseck Mountain (peak elevation 2,711 meters) is located on the western side of the Lower Tauerns (Niedere Tauern), a part of the eastern Austrian Alps. The Lower Tauerns are a result of the African and European tectonic plates colliding, which began in the Jurassic and continues today. A nappe or thrust-sheet structure of schists and limestones created by this event typifies the area’s geology. It has long been known that the white, karst (cavern-filled) Felsgestalt limestone unit in the Lower Tauerns is associated with fluorite mineralization at Weisseck. The white (Weiss) color of the limestone gave the mountain its name. Dissolution of the limestone created openings which allowed the formation of fluorite crystals.

Schwarzsee 2013 113a.jpg

View to Weisseck east side (photo Lasshofer Hans)

HISTORY

The Weisseck Mountain area has long been famous for fine fluorite specimens. The first volume of Viktor von Zepharovich’s Mineralogisches Lexicon für das Kaiserthum Österreich (“Mineralogical Lexicon of the Austrian Empire”) (1859; covering the years 1790–1857) mentions pale blue to violet-blue fluorite cubes from Weisseck. Ludwig Ritter von Köchel’s Die Mineralien des Herzogthumes Salzburgs (“The Minerals of the Dukedom of Salzburg”) (1859) also mentions fluorite discoveries at Weisseck Mountain. The mineral collections of the House of Nature museum in Salzburg and the Museum of Natural History in Vienna contain documented crystals from the classic finds of the 19th century. Provenance questions existed even in those early days, as von Köchel regarded certain specimens labeled “Konigstuhlhorn, Rauris” as more likely being from Weisseck, indicating his depth of knowledge concerning the morphology of the area’s specimens. Since those early explorations, additional cavities in the hard limestone and dolomite marbles of the area continued to be discovered. In the 1980s, a group of Viennese collectors discovered a fluorite pocket near Lake Rieding on the northwest flank of Weisseck Mountain, 600 meters below the summit. The fluorite they recovered is in the form of green and violet cubes, most with matte luster and measuring 2 to 3 cm on edge, intergrown and as individual crystals on a limestone matrix. A few exceptional specimens showing crystals to 5 cm with bright luster were also recovered, along with some fluorite of an unusual aquamarine color.

Summit Cleft 2001

WE 1 (2).JPG

Lower entrance to the large Summit Cleft

In the beginning of July 2001 a group of Strahler from Lungau, including myself, managed to open up another cleft through a passage of clay. The large Summit Cleft was discovered! (See Mineralogical Record, Vol 41, #4 (July-August) 2010 for a more detailed account). For me, these excavations provided the start of my long-term relationship with Weisseck fluorites.

WE 1  (2).JPG

The small passage was completely filled with clay originally

Once we removed the clay, which had aged there for decades, we found a vein rising slightly upwards. The passage covered in clay is around 4 meters long. In the end of the passage, we found a pinewood chip (a wood chip soaked in bitumen used as source of light in the Middle Ages). In this area we also found the first beautiful fluorite specimens. All the crystals in this area had loosened from the rock and lay partly covered with clay on the floor. I was at the forefront of the first collection tours and was able to experience first-hand how the first fluorites were recovered.

a (16).JPG

Newly salvaged intergrown dice of fluorite

a (5).JPG

 Newly salvaged intergrown dice of fluorite, photographed outdoors

During the later tours I worked in the middle area. My task was to pull a flat-cut canister (hunt) out of the slit using a rope. I then emptied this into another hunt, which was then pulled outside by another collector. The hunt was emptied outside and then pulled back in by me. This work often continued for hours to remove all the rubble.

2001 Plan Gipfelkluft English.jpg

 Discovery area marked in blue, immediately after the clay passage

In 2001 I participated in twelve tours to the cleft. Since we needed at this time to keep the find secret, we did not follow the usual hiking trail. The Muritzen car park was our starting point. From there we followed the forest road towards Sticklerhütte. Halfway to the Sticklerhütte, we branched off on a small climb towards Göllalm (towards Plankowitzspitze), in order to climb as unnoticed as possible from there to the Weisseck. At the point where we turned off the forest road, we hid a two-wheeled vehicle specially designed by one of the collectors. This transport device could accommodate all five backpacks on the way back. Two people pulled in front, two helped with belts attached to the side. In retrospect, I am surprised that we were never approached by hikers about our unusual vehicle. After each of these tours, the fluorites were washed at a collector's home and then were divided.

WE 1-2, 12 x 10 x 8 cm (1).jpg

My first tug after the first tour: a perfect twinned cube, 6.5 cm edge length – not bad for the first time at the Summit Cleft!

Many fluorites show an intense square texture and on the edges a stair-like structure. Some fluorites are dark purple and reveal little color. But when illuminated from behind, they dazzle with both deep colors and pastel shades. 

WE 1-2, 12 x 10 x 8 cm (2).jpg

The same specimen with backlit, 8 x 12 x 10 cm

WE 1-5, 14.5 x 12 x 7.3 cm (2).jpg

Undamaged fluorite cubes up to 6.5 cm, three-dimensional grown on some limestone, 14.5 x 12 x 7.3 cm

WE 1-7, 12 x 11 x 7 cm (1).jpg

Fluorite with remarkable edge length of 8.5 cm, 12 x 11 x 7 cm

WE 1-11, 12 x 12 x 8.5 cm.jpg

This piece was published in the Mineralogical Record, 41, 4 (July issue 2010), 12 x 12 x 8.5 cm (photo: Watzl Anton Sen.)

Some specimens came from the area of the small passage: quartz matrix composed of small, high-gloss needle quartz and transparent fluorite cubes with intensive zoning. Most of these pieces were destroyed by the frost.

WE 1-3, 8.5 x 5.5 x 3.5 cm (1).jpg

Fluorite cubes with intensive zoning on high-gloss needle quartz, 8.5 x 5.5 x 3.5 cm

Some fluorites from the upper area show a hint of pink to an intense purple color in the center and a cyan zoning on the edges. The maximum edge length for this type of fluorite is 4 cm.

WE 1-9, 12 x 8.5 x 5 cm (1).jpg

Undamaged fluorite with satiny luster and intense square texture, 12 x 8.5 x 5 cm

WE 1-13, 21 x 23 x 10 cm (1).jpg

This fluorite comes from the last collecting tour at the Summit Cleft in October 2001, 21 x 23 x 10 cm