[5] It occurs as argillaceous inclusions in volcanic rocks in the Isle of Mull, inclusions in sillimanite within a tonalite at Val Sissone, Italy and with emerylike rocks in Argyllshire, Scotland.

[3] Mullite (porcelainite) can be found as a constituent mineral in a type of thermally-metamorphosed rock called porcellanite.

[11][12] The formula finally replicated in the above studies (using kaolinitic clay and then firing it at temperatures above 1100 °C) was kept a closely guarded secret by those crucible makers since the 15th century.

If the needle shape mullite can form in a ceramic body during sintering, it has an effect on both the mechanical and physical properties by increasing the mechanical strength and thermal shock resistance.

[13][14] Further recent research indicates that a synthetic analogue of mullite can be an effective replacement for platinum in diesel engines for exhaust management.