What exactly is petuntse, the "china stone" used as one of two ingredients in porcelain along with kaolin?
The Wikipedia article (and books I have read) describe petuntse as a mineral containing feldspar. Well, fine, but there are a lot of minerals that are certainly not petuntse that contain feldspar. Feldspar is one of the most common minerals, so saying it is a material with feldspar in it, is not specific.
What is the specific composition of traditional petuntses used to make porcelain?
According to the Pottery Histories web site:
Petuntse
Petuntse is a historical Chinese term for rocks with a high content of mica and feldspathic minerals that have been used as one of the ingredients in the manufacture of Chinese porcelain. It is generally similar in composition and use to China stone. Petuntse, with china clay, forms the base ingredients for hard-paste porcelains similar to those produced in China in historic times. See China stone.
and
China stone (Cornish stone, Cornwall stone)
China stone is a feldspar-rich mineral derived from partially decomposed granite. China stone includes feldspar, mica, fluorospar, quartz and other granite-derived minerals such as kaolinite, but lacks iron-bearing minerals. China Stone is used worldwide as a flux in the manufacture of ceramic bodies and glazes. In the United Kingdom, the material is mined in one small area of Cornwall.
I don't know if this meets the degree of specificity that you were looking for.
