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Grube Clara baryte - A wealth of habits and colours

Last Updated: 27th Feb 2019

By Niels Brouwer

The Black Forest, an age-old region in the southwest of Germany that combines breathtaking vistas with remarkable mineral finds from the area’s exceedingly long and rich mining history. There is documentary evidence that the location of Grube Clara has been scoured for its mineral wealth since at least as far back as 1652, with the mine name Clara documented as early as 1726. Most likely mining on this mountain near the town of Oberwolfach dates back even further to medieval or Roman times, ample time for a multitude of legends to arise, be retold and embellished.

According to one of these myths, in days of old the prosperous mining city of Benau was situated here – so prosperous in fact, they had forsaken their christian faith and instead venerated a silver or golden calf that was the source of all their riches. Upon discovering this, God completely levelled the city and buried the calf deep in the ‘Benauer Berg’ (Benauer mountain). Ever since, miners have attempted to discover the hidden treasures buried deep within the rock.

1. Clear chisel-shaped crystals with interesting phantoms, caused in part by yellow colour zoning and partly by granular brown inclusions. 14,2 x 7,1 cm.


Although gold and silver may no longer be the main aim, people still come here to try their luck. Many mineral enthusiasts visit the mine’s specially designated stockpiles in a search to enrich their collection with one of the more than 400(!) different mineral species that have been identified so far. But besides these numerous (micro)minerals, the Grube Clara is also well-known for the multitude of exceptionally fine baryte specimens.

2. Pink tabular baryte on crystal clear cubic fluorite. 6,0 x 5,2 cm.


Chequered geological past


The Grube Clara is situated amidst the picturesque wooded mountainous surroundings that typify the Black Forest. At one time, the region was still connected to the Vosges region (now situated across the border in France) but geological activity drove the two apart, opening up the wide valley in between them through which the river Rhine now flows. The same process also lifted the mountain tops in the Black Forest upwards and caused faults and fissures to appear deep within its rocks. Once the upper layers of rock had been eroded away, groundwater was able to reach these faults, carrying the elements that precipitated to form the minerals that we now treasure. In a way, the grandeur and beauty of the surrounding landscape is a fitting reminder of the processes that led to the formation of these very delicate minerals.

3. Stack of clear parallel blocky baryte crystals, included with intricate 'clouds' of goethite. 5,7 x 4,0 cm.
4. Upstanding 'Meißelspat' crystal, partly covered by a second generation of smaller crystals. 6,7 x 4,2 cm.
3. Stack of clear parallel blocky baryte crystals, included with intricate 'clouds' of goethite. 5,7 x 4,0 cm.
4. Upstanding 'Meißelspat' crystal, partly covered by a second generation of smaller crystals. 6,7 x 4,2 cm.
3. Stack of clear parallel blocky baryte crystals, included with intricate 'clouds' of goethite. 5,7 x 4,0 cm.
4. Upstanding 'Meißelspat' crystal, partly covered by a second generation of smaller crystals. 6,7 x 4,2 cm.


Crystal formation


In contrast to the ancient copper, silver and gold mining history, the current mine employs very modern techniques to extract the baryte and fluorite. For some years now, the level on which they operate has reached below sea level, more than 900 meters below the top of the mountain. For a period of time they also worked the Schwarzenbruch, an opencast section of the mine, but this has now been closed again for several decades.

5. Cluster of parallel baryte crystals ranging from vivid blue to pinkish red. Found in 19772 in the Schwarzenbruch. 9,5 x 7,0 cm.


The veins they are working extend for a length of 600 meters and are divided in three parts. The baryte and fluorite veins (named after the respective minerals that are most abundant) run mostly parallel to each other; at a later stage, the ‘Diagonaltrum’ vein has bisected these two veins. Each of these veins has a distinctly different composition of minerals, with the sections where they intersect further increasing the mineralogical diversity.

6. Unusual frosted radial formation of slender Meißelspat. 8,1 x 5,6 cm.


Baryte habits


For the formation of baryte, three main phases can be distinguished (see below for further explanation of the German terms):

1. ‘Messerspat’-phase: tabular, opaque white crystals; commonly as massive veins, but rarer as well-formed freestanding crystals.
2. ‘Honigspat’-phase: light to brownish yellow crystals, often translucent or transparent; found as tabular, blocky or chisel-shaped crystals, generally quite rare.
3. ‘Meißelspat’-phase: clear, distinctively chisel-shaped crystals, but a wide variety of blocky, tabular and prismatic crystals are also commonly found. They regularly display beautiful phantoms, colour zoning, modifications, inclusions and parallel growth.

Specimens that show crystals from two of these three phases are quite common, but specimens with all three present are fairly rare.

The aforementioned impressive dimensions of the mineralised veins, both in length and depth, gave rise to significant differences in temperature, pressure, concentration of the mineral fluids, flow rate, etc. This has led to an impressive variation of different baryte habits, crystal sizes, combinations with other minerals, and so on.

7. A combination of baryte from all three crystallisation phases. 14,4 x 12,3 cm.


Nicknames


With such a wealth of different shapes and sizes of baryte, the miners and collectors have used a multitude of nicknames to distinguish them.

- Messerspat, 'knife spar'; baryte from the first mineralisation phase, which due to its thin, flat shape with tapering edges is reminiscent of a knife.
- Honigspat, 'honey spar'; second phase baryte with a distinctive honey colour. Confusingly, elsewhere this term is also in use for fluorite with the same golden yellow colour.
- Meißelspat, 'chisel spar'; baryte from the third phase, named after the pointed crystals that look like the tip of a stone chisel.
- Walmdach-form; a crystal habit that resembles the clipped gable roofs of the characteristic Black Forest farmhouses.
- Schwerspat, 'heavy spar'; old term for the mineral baryte after its high density.
- Sauzahne, 'pigs teeth'; tapering, slightly rounded baryte crystals, found in large quantities on the 10.2 level around 1992.
- 76er-Baryt; from 1976 to '78, a few interconnected pockets were found on the 9.0 level, filled with particularly well-formed chisel-shaped crystals, often with marvellous colour zoning.
- Schwarzen Peter, 'Black Pete'; dark, sometimes somewhat purple, thin chisel-shaped crystals from the 76er style, coloured by inclusions of manganese oxides. These were only found in the last of the interconnected pockets in 1978 and are exceedingly rare.
- Elfnuller-Baryt, 'eleven zero baryte'; thick, blocky baryte found on the 11.0 level in 1997.


8. Example of the rounded crystals of the 'Sauzahne' habit. 6,6 x 5,6 cm.
9. Cluster of pink double terminated Meißelspat. 6,5 x 5,5 cm.
8. Example of the rounded crystals of the 'Sauzahne' habit. 6,6 x 5,6 cm.
9. Cluster of pink double terminated Meißelspat. 6,5 x 5,5 cm.
8. Example of the rounded crystals of the 'Sauzahne' habit. 6,6 x 5,6 cm.
9. Cluster of pink double terminated Meißelspat. 6,5 x 5,5 cm.


10. Sharply pointed crystals in varying shades of beige due to inclusions of pocket clay. 6,1 x 5,2 cm.
11. Tabular white Messerspat overgrown by dark goethite, along with a clear cubic fluorite crystal. 11,3 x 6,6 cm.
10. Sharply pointed crystals in varying shades of beige due to inclusions of pocket clay. 6,1 x 5,2 cm.
11. Tabular white Messerspat overgrown by dark goethite, along with a clear cubic fluorite crystal. 11,3 x 6,6 cm.
10. Sharply pointed crystals in varying shades of beige due to inclusions of pocket clay. 6,1 x 5,2 cm.
11. Tabular white Messerspat overgrown by dark goethite, along with a clear cubic fluorite crystal. 11,3 x 6,6 cm.


12. Clear blocky crystals, grown on a core of yellow Meißelspat. 11,4 x 9,9 cm.
13. Freestanding golden yellow Honigspat with Meißelspat crystal shape. 10,4 x 8,3 cm.
12. Clear blocky crystals, grown on a core of yellow Meißelspat. 11,4 x 9,9 cm.
13. Freestanding golden yellow Honigspat with Meißelspat crystal shape. 10,4 x 8,3 cm.
12. Clear blocky crystals, grown on a core of yellow Meißelspat. 11,4 x 9,9 cm.
13. Freestanding golden yellow Honigspat with Meißelspat crystal shape. 10,4 x 8,3 cm.


14. Clear Honigspat with interesting crystal habit and distinct phantoms. 9,3 x 8,0 cm specimen, field of view 22 mm.
15. Transparent, extremely lustrous crystals on a coarse white baryte matrix. 7,5 x 4,6 cm.
14. Clear Honigspat with interesting crystal habit and distinct phantoms. 9,3 x 8,0 cm specimen, field of view 22 mm.
15. Transparent, extremely lustrous crystals on a coarse white baryte matrix. 7,5 x 4,6 cm.
14. Clear Honigspat with interesting crystal habit and distinct phantoms. 9,3 x 8,0 cm specimen, field of view 22 mm.
15. Transparent, extremely lustrous crystals on a coarse white baryte matrix. 7,5 x 4,6 cm.


16. Crystal clear Meißelspat. 4,9 x 3,5 cm.
17. Sauzahne, coloured brown due to inclusions in the crystals. 16,3 x 9,8 cm.
16. Crystal clear Meißelspat. 4,9 x 3,5 cm.
17. Sauzahne, coloured brown due to inclusions in the crystals. 16,3 x 9,8 cm.
16. Crystal clear Meißelspat. 4,9 x 3,5 cm.
17. Sauzahne, coloured brown due to inclusions in the crystals. 16,3 x 9,8 cm.


18. White tabular Messerspat, covered by a thin patchwork of red and black hematite. 3,3 x 3,3 cm.
19. Clear blocky crystals, with inclusions of pocket clay only at the tips of the crystals. 13,5 x 9,4 cm.
18. White tabular Messerspat, covered by a thin patchwork of red and black hematite. 3,3 x 3,3 cm.
19. Clear blocky crystals, with inclusions of pocket clay only at the tips of the crystals. 13,5 x 9,4 cm.
18. White tabular Messerspat, covered by a thin patchwork of red and black hematite. 3,3 x 3,3 cm.
19. Clear blocky crystals, with inclusions of pocket clay only at the tips of the crystals. 13,5 x 9,4 cm.


20. Transparent baryte crystals with a golden yellow core, revealing the yellow Honigspat as an earlier phase. 11,5 x 6,5 cm.
21. Sharp wedge-shaped crystals, overgrown on one side with a layer of tiny pointy crystals. 6,3 x 5,3 cm.
20. Transparent baryte crystals with a golden yellow core, revealing the yellow Honigspat as an earlier phase. 11,5 x 6,5 cm.
21. Sharp wedge-shaped crystals, overgrown on one side with a layer of tiny pointy crystals. 6,3 x 5,3 cm.
20. Transparent baryte crystals with a golden yellow core, revealing the yellow Honigspat as an earlier phase. 11,5 x 6,5 cm.
21. Sharp wedge-shaped crystals, overgrown on one side with a layer of tiny pointy crystals. 6,3 x 5,3 cm.


22. Grey razor-sharp Meißelspat, showing an interesting second crystallisation layer that only partly covers the crystals. 13,7 x 7,2 cm.
23. Pointed Meißelspat with beautiful yellow colour zoning. 9,2 x 8,4 cm.
22. Grey razor-sharp Meißelspat, showing an interesting second crystallisation layer that only partly covers the crystals. 13,7 x 7,2 cm.
23. Pointed Meißelspat with beautiful yellow colour zoning. 9,2 x 8,4 cm.
22. Grey razor-sharp Meißelspat, showing an interesting second crystallisation layer that only partly covers the crystals. 13,7 x 7,2 cm.
23. Pointed Meißelspat with beautiful yellow colour zoning. 9,2 x 8,4 cm.


24. Large cluster of clear Meißelspat with yellow cores, on massive white baryte matrix. 11,2 x 8,4 cm.
25. White Messerspat with clear cubic fluorite and quartz. 7,3 x 6,6 cm.
24. Large cluster of clear Meißelspat with yellow cores, on massive white baryte matrix. 11,2 x 8,4 cm.
25. White Messerspat with clear cubic fluorite and quartz. 7,3 x 6,6 cm.
24. Large cluster of clear Meißelspat with yellow cores, on massive white baryte matrix. 11,2 x 8,4 cm.
25. White Messerspat with clear cubic fluorite and quartz. 7,3 x 6,6 cm.




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Comments

Out of curiosity, have you checked for fluorescence?

Keith A. Peregrine
28th Feb 2019 10:27pm
Yes, I have certainly checked them for fluorescence under longwave UV light, but I have yet to come across any baryte specimen from Grube Clara that displays this.

I know that through dissolution and recrystallisation between the various phases, the strontium content in the baryte gradually markedly decreases; concentrations of other inclusions will most likely vary as well. In other localities, the most common activator in fluorescent baryte appears to be uranyl ions, but despite the ample uranyl-bearing microminerals found in this quarry, it does not appear to be included in significant amount in the baryte to cause fluorescence. Combinations with, and inclusions by, numerous secondary minerals during these processes are also widely featured in collections and the photos here on Mindat, so it wouldn't have been unthinkable that elements would have been included as activators of the fluorescence. However, it simply appears not to have happened that way.

If anyone else does have specimens that show fluorescence, or have a more detailed explanation for the lack of it, I would certainly be very interested to hear it.

Niels Brouwer
1st Mar 2019 12:53am
Niels
Beautiful photos - thanks for sharing.
Cheers

Keith Compton
2nd Mar 2019 12:29pm
Thanks for your observations, Niels.

Keith A. Peregrine
2nd Mar 2019 8:23pm
Keith & Keith, thanks for your kind comments.

Niels Brouwer
3rd Mar 2019 6:21pm
Nice article!

Uwe Kolitsch
14th Mar 2019 12:53pm

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