Ceramics of indigenous peoples of the Americas
The clay body is a necessary component of pottery. Clay must be mined and purified in an often laborious process, and certain tribes have ceremonial protocols to gathering clay. Different tribes have different processes for processing clay, which can include drying in the sun, soaking in water for days, and repeatedly running through a screen or sieve. Acoma and other Pueblo pottery traditionally pound dry clay into a powder and then remove impurities by hand, then running the dry powder through a screen, mixing it with a dry temper, and then mixing water to create a plastic paste. In preparing the clay, potters spend hours wedging it to remove air pockets and humidity that could easily cause it to explode during firing. The clay then needs to "cure" over time.
Geology of Cornwall
Extraction of tin began in Cornwall in prehistoric times and continued until the late 20th century. Historically extensive tin and copper mining has occurred in Devon and Cornwall, as well as arsenic, silver, zinc and a few other metals. Granite, slate and aggregate are still quarried and china-clay extraction continues on a large scale. 
There are ample supplies of granite worth the cost of shipping out of the county and much Cornish granite has been used in distant places. It is one of the most appropriate materials for memorials and examples are found in most parts of Cornwall. there are no active metalliferous mines remaining. However, tin deposits still exist in Cornwall, and there is talk of reopening South Crofty tin mine.