The steady and sharp fall in coal prices has knocked down shares of big mining companies like BHP Billiton (NYSE: BBL - news ) , Glencore (Xetra: A1JAGV - news ) and Rio Tinto (LSE: RIO.L - news ) , and it has seen many financers exit the sector.
Refer to the input text as context and select the correct relationship between 'Glencore' and 'mining' from the available options.
Options: product/material produced, stock exchange, chairperson, industry