I've never heard of Porcelain Stone. The wikipedia article on Porcelain doesn't mention anything called Porcelain Stone. Reading some articles surrounding Porcelain led me to Peuntse (https://en.wikipedia.org/wiki/Petuntse) and I wonder if this is Porcelain Stone?
Yes, it's also known as petuntse. Excerpt from Chinese Art by Stephen W. Bushell, 1910:
Porcelain has been broadly defined as the generic term employed to designate all kinds of pottery to which an incipient vitrification has been imparted by firing. This translucent pottery may be divided into two classes: 1. Hard paste, containing only natural elements in the composition of the body and the glaze. 2. Soft paste, where the body is an artificial combination of various materials agglomerated by the action of fire, in which the compound called a frit has been used as a substitute for a natural rock. No soft paste porcelain, as here defined, has ever been made in China, so that it need not be referred to further. All Chinese porcelain is of the hard paste variety. The body consists essentially of two elements-viz., the white clay, or kaolin, the unctuous and infusible element, which gives plasticity to the paste, and the felspathic stone, or petuntse, which is fusible at a high temperature, and gives transparency to the porcelain.
Of the two Chinese names, which have become classical since they were adopted in the dictionary of the French Academy, kaolin is the name of a locality near Chingtêchên where the best porcelain earth is mined, petuntse, literally "white briquettes," refers to the shape in which the finely pulverized porcelain stone
is brought to the potteries, after it has been submitted to the preliminary processes of pounding and decantation. The felspathic stone from Ch'i-mên-hsien, in the province of Kiangsu, has been chemically analysed by Ebelmen, who describes it as a white compact rock of slightly greyish tinge, occurring in large fragments covered with manganese oxide in dendrites, and having crystals of quartz imbedded in the mass, which fuses completely into a white enamel under the blowpipe.
