Thread: Thuringian Waterwhetstones – some interesting geological issues

When we talk about the soft Thuringian Waterwhetstones like the Escher labeled stones we are talking about slate stones. The stones exist more precisely of mud-slate, a material that was built as deposits of a deep, calm see. Minerals and plants sank to the ground, were covered by mud and through millions of years these slate stones were build with temperature and pressure of the earth tectonics.

People often don’t like to hear that these stones are made of slate, a material that is used for house building and other common things. But if you have once been in the slate mountains of Thuringia and see all this slate rocks over thousands of square miles and then remember that there are only very small quarries were you could have found this wonderful stuff that fits exactly for a whetstone – it’s fantastic!

It might be interesting to hear that the slate horizons in these quarries consist of up to 250 different layers consisting of pure whetstone layers, simple mud-slate layers, brown slates greywacke and finally quartz layers. About 160 layers were defined as pure whetstone layers but at the end less than maybe two dozen of them were feasible and could be used to make whetstones. The layers in total had all different thinkable colors from yellow-white through green, blue also reddish and brow to black.
For the original Thuringian Waterwhetstones only the yellow, green and blue layers were mined. They were divided into the well know quality levels yellow green – light green – blue green and (dark) blue.

There is often the question if yellow layers exist and the answer is a straight yes. There are about 6 yellow layers the miners had given names too, so they surely had been of good quality and were quarried as whetstones. Some expressive names were “flammiger Gelber” or “Markasitengelber” or also “Tuffengrüner”.
The yellow stones were also sold under the quality yellow-green, I don’t have seen a label yellow in all the times. But I also think that all qualities contain not simply one layer (color), but a certain range of colors. So the yellow green quality contains whitish, yellow and soft green ones, the light green quality stands more for all shades of gray, etc.
The most special quality for me seems to be the blue-green stones because they are indeed very special colored and I also think they are the most rare ones to find.

That quartz layers are existing next to the whetstone slates is comprehensible, because quartz particles are the abrasive material in the whetstones. But you can see the quartz layers are really “docking” on the slate layers sometimes. The following picture shows an example:




A perfect two toned natural combination whetstone light green – blue that was cut for whetstones until the quartz layer was reached. You can also see the natural perfect straight sharp end of the stone were the quartz is sitting on.





On the backside you can see the typical horny layer that contains a lot of iron as oxide, sulphide and elemental too.