Mullite

Mullite, or porcelainite, is a rare clay mineral, aluminum silicate (Al₆Si₂O₁₃). It is produced artificially during various melting and firing processes, and is used as a refractory.

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Researchers recently discovered ^[1] that potters in the Hesse region of Germany unknowingly used mullite to create crucibles, enabling alchemists to heat their crucibles to very high temperatures. The formula for making it (using kaolinitic clay and then firing it at temperatures above 1100 degrees) was kept a closely guarded secret.

Mullite is present in the form of acicular crystals in porcelain.

References

1. ^ University College London, November 23, 2006, retrieved November 24, 2006.