The Duchy owns many quarries, mainly in the High Peak areas of Derbyshire, from which the following minerals are extracted: barytes  (a source of barium); calcite (calcium carbonate); coal; fluorspar (calcium flouride); gravel; gritstone; gypsum (hydrated calcium sulphate used for making plaster and cement); lead; limestone; salt; sand; sandstone; stone. 

The Duchy Mineral Agent is appointed as a consultant to obtain the best use and value of minerals on lands owned by the Duchy. He inspects the areas where minerals are being mined and provides the Duchy with advice as required and submits a full report each year. He acts as the middle-man in rental agreements and royalty negotiations between mining companies and the Duchy Surveyors of Lands. The Mineral Agent also investigates ownership rights being contested.

The post is currently held by Mr. E.T. Tennant, of Coke, Turner & Co who was appointed in January 1999 for a three-year term (renewable).