Giant crystals often occur in remote areas, which are difficult
to visit even these days. Others are protected with only very restricted
access or are on private property. Or they are simply mined out since long time.
The Merkers potash mine is different.
If you feel in the right mood to experience an outstanding underground mine, you can
go down the Merkers shaft. Apart from the thrill of experiencing a preserved
potash mine with its fascinating machinery and the reconstructed
"gold vault" of the Third Reich you are allowed to have a good look into
the largest known salt crystal cave in Middle Europe.
Halite salt rock is generally a very ductile type of rock, that is, under pressure
it tends to flow quite easily. An old stope in a salt
mine may completely shrink to a mere small hole in just a hundred years time
due to salt flowing. So the miners in the 750 m deep Merkers mine were
quite surprised when they found a large natural cave at that depth. More - the cave was partly
filled with giant halite cubes up to more than 1 m edge length.
Knowing, that the government of socialistic East Germany always was
keen to sell outstanding mineral specimen in exchange for hard Deutschmark to the west, the miners deciced
to seal off the opening to the cave and wait for better times.
After the collapse of the GDR in 1990 the cave was opened again and,
while potash production in the mine was curtailed and finally stopped,
it was decided to turn the whole mine into a public museum. So here we are :
one of the very few giant crystal localities which is a dedicated tourist
attraction : the Erlebnisbergwerk Merkers.
The formation of this extraordinary halite cubes is - notwithstanding
their size - quite simple. Whereever there is free space in a salt mine,
the ubiqitious migrating salt brines tends to crystallize on the walls of this space.
Mostly these crystals are only small due to the small space available.
In this case the available space was large and so the crystals could grow
to giant dimensions, not even filling up the whole
Finally it has to be said, that similar halite cubes were apparently
found in other salt deposits as well. RÖSLER (1980) notes 'salt cubes
of 100 cm' from the Allertal potash mines in northern Germany and from
Detroit / USA, but dont give any closer details. More information is available about giant
"golden" halite cubes in New Mexiko, which can be found here.