Treak Cliff Cavern is known for its geological importance. It has been a designated Site of Special Scientific Interest for many years and by agreement with English Nature all the Blue John Stone deposits on the visitor route are preserved. Blue John Stone is the most prized ornamental variety of Fluor-Spar (Calcium Fluoride). Differing from any other flour-spars in that it has definite banded veins of colour running through it.
Blue John Stone, however, is regularly mined in Treak Cliff cavern from areas not seen by visitors. This is then crafted into fine jewellery, small bowls, ornaments and other decorative items which can be bought from Castleton village.