15
Living Stones
The Feengrotten are unique because their dripstones consist predominantly of the rare mineral diadochite and not limestone. Due to the special water conditions in the grottoes, these formations grow significantly faster than dripstones in conventional limestone caves.
Learn more:
Learn more:
In the tunnels of the former “Jeremias Glück” mine, alkaline deep water meets acidic water from near-surface layers. These special underground water conditions are the reason why the Feengrotten were able to develop into the most colorful show grottoes in the world.
Dripstones usually form in limestone caves. There, carbonic acid-containing seepage water dissolves the limestone and transports the dissolved calcium carbonate into the cave. Tiny limestone crystals remain on the cave ceiling with each drop of water, from which dripstones grow over a long period.
This process is extremely slow: it takes more than a hundred years for a limestone dripstone to grow between eight and fifteen millimeters. A dripstone one meter long therefore requires around ten thousand years. In dry periods, growth even comes to a complete standstill.
There are also limestone dripstones in the Feengrotten. However, they are rare, as the predominantly acidic to strongly acidic water prevents calcium carbonate from depositing.
Most dripstones in the Feengrotten consist instead of the soft mineral diadochite. Under the special conditions of the grottoes, they grow up to three centimeters per year – a length
Try it yourself:
Can the growth of dripstones be accelerated by more water dripping on them? What role does the pH value of the water play? And how do the vibrant colors of the Feengrotten come about? Here you can try it yourself and discover which factors influence the growth of dripstones.
pH value
The pH value indicates whether an aqueous solution is acidic, neutral, or alkaline. In a cave, it determines whether dripstones grow or dissolve. A slightly acidic to alkaline pH value – roughly between 6 and 14 – promotes growth. However, if the water is strongly acidic, i.e., at a pH value below 3, the dripstones are slowly decomposed.
Water supply
The amount of water also plays a crucial role. If a lot of mineral-rich water enters the cave, dripstones can grow. If, on the other hand, only a little water flows in, their growth slows down or comes to a complete standstill.
Minerals
The dripping water in the Feengrotten also contains various metals and other dissolved substances. These form new minerals that give the dripstones their extraordinary colors.
- Diadochite: Dripstones made of pure diadochite are white to light yellow.
- Copper compounds: They color the dripstones blue or green.
- Iron compounds: They produce rusty red to brown hues, sometimes also yellow.
- Manganese compounds: They provide brown-black to deep black colorations.
- Vanadium compounds: They produce various shades of green – from yellow-green to olive green to apple green.