Pyrophyllite is a clay mineral composed of aluminum silicate hydroxide Al2Si4O10(OH)2, a member of the family of layered double hydroxide. It generally occurs as thin tabular crystals, usually in foliated masses, the crystals being rarely prismatic. It has a Mohs hardness of 7 and a specific gravity of 2.75-2.91.
Pyrophyllite has been mined for centuries for use as a ceramic material. It is composed of thin flaky crystals that are highly compatible with both alumina and zirconia containing glazes, resulting in an excellent balance of strength and durability. It is used in pottery and porcelain in up to 25-30% in many formulations. Its excellent refractory properties give it a distinct advantage in ceramic glazes. The reason for its widespread use is its exceptional compatibility with other glaze materials, making it a low-toxicity substitute for lead in combination with high amounts of alumina (Al2O3).
Pyrophyllite has a long history in Asia, especially in Japan, where it was first mined by early Jomon period people some 3,000 years ago. In recent years, the deposits in Shanxi and Hunan provinces in China have become major sources of pyrophyllite. The crystal clusters are usually white in color, and can have a range of colors such as light yellow, light green, light blue and pink.
Pyrophyllite has a wide range of applications. It is widely used for the production of glazes, ceramic tiles, electrical insulation, paint, paper, carborundum, and stoneware tiles. It can be used as a fillers for asphalt, rubber, and plastics, and as a binder for cements and adhesives. Pyrophyllite has also been used in the manufacture of catalysts, filter aids, and refractory products. Due to its low melting point, it has been used for the manufacture of fire extinguishers.
Pyrophyllite is relatively soft, and as such can be used in combination with stoneware clays or fireclay in order to give an additional boost to their strength and working characteristics. This combination can be used to produce a much stronger tile or dinnerware than either material alone.
Pyrophyllite is also well-suited to the production of high-quality pottery and porcelain, where its low thermal expansion makes it resistant to large temperature fluctuations. Its low pH also makes it an ideal material for the manufacture of wall tiles and floor tiles, as it can be used without fear of corrosion. The combination of its high compressive strength, electrical insulator properties, and good water-resistance make it well suited for the manufacture of a variety of ceramic products.
In conclusion, pyrophyllite is a versatile mineral with a wide range of applications. Its low pH and thermal expansion properties make it ideal for the manufacture of high-quality ceramics, tiles, and various other products. Its compatibility with alumina and zirconia containing glazes give it an advantage over other materials, and its low toxicity make it an attractive alternative to lead-based glazes. Overall, pyrophyllite is an important mineral and has numerous beneficial applications.
