The Blue John Cavern
The Mining Of Blue John Stone
Mining is essentially
done by hand. Blasting is resorted to only very occasionally in special
circumstances, as the shock can disturb the crystalline structure and render
the stone incapable of being worked. Blasting can shock the characteristic
colouring and banding out of the stone and render the fluor-spar an off-white
opaque colour. Even if the crystalline structure is still sound the discoloured
material is worthless.
When the Blue John occurs in nodules it is relatively easy to dislodge the fungus like formation with hammer and chisel and crowbars but great care is required to remove the nodules without damaging them. These nodules are not easily recognisable to any but the most experienced as they are normally completely buried in clay. The miners recognise a lump of Blue John by its weight. It is the nodules that are greatly prized as the configuration is in concentric bands.
Often the Fluor-spar occurs in ganges, or veins surrounded by limestone needing a more complex process to remove them. The extremities are sought and with a crow bar and chisel the miners cuts a deep ledge above the entire deposit. however the depth of the hole is pure guess work as the miners don't know the depth of the deposit The ledges are extended downwards at the lateral extremities to a suitable bedding plane beneath the fluorite. The final phase in the mining known as "lifting". Wedges and crowbars are carefully driven into the bedding plane beneath the deposit. The entire piece is lifted out, all excess material is carefully removed and the true size of the find is only then discovered.
The cavern guides do the Mining and cavern maintenance during the winter months. Craftmen spend the year at our workshop in Castleton making the jewellery.