Mullite
Definition
An aluminosilicate phase (3Al2O3·2SiO2) that nucleates in fired clay above roughly 980 °C, coinciding with the characteristic exothermic reaction of the kaolinite-to-mullite transformation sequence; its presence in a ceramic records a high-temperature firing and kiln technology capable of sustained elevated temperature.
- Formula
- 3Al2O3.2SiO2
- Formation threshold
- Roughly 980 degrees C
- Precursor reaction
- Kaolinite-to-mullite transformation
- Reaction type
- Exothermic
- Evidential meaning
- Confirms high-temperature kiln firing
Common questions
How does mullite help date or source a fired-clay object?+
Its presence or absence brackets the firing temperature the object experienced, so comparing mullite content between a questioned brick or ceramic fragment and a suspected source kiln can support or rule out a common origin.
What method detects mullite in a ceramic sample?+
X-ray diffraction is the standard identification technique, since mullite has a distinct crystal structure that separates it from the unfired clay minerals and other high-temperature phases like cristobalite.
Related terms
- Ceramic Fabric
- The combination of clay matrix and included particles (temper, natural inclusions, and voids) that makes up a fired ceramic; the raw material...
- Dehydroxylation
- The loss of structural hydroxyl groups from clay minerals (principally kaolinite) between about 450 and 600 °C during firing; an irreversible reaction...
- Grog
- Crushed fragments of previously fired ceramic mixed into new clay as temper; recognisable in thin section by their fired-clay texture, which differs...
- Provenance
- The documented origin of a media file: the device that captured it, the time and location of capture, the chain of custody...
- Temper
- Material deliberately added to clay before forming to reduce drying shrinkage and firing cracking; common temper types include sand, grog (crushed old...