Mullite
A variety of Minerals
What is Mullite?
Mullite or porcelainite is a rare silicate mineral of post-clay genesis. It can form two stoichiometric forms: 3Al2O32SiO2 or 2Al2O3 SiO2. Unusually, mullite has no charge-balancing cations present. As a result, there are three different aluminium sites: two distorted tetrahedral and one octahedral. Mullite was first described in 1924 for an occurrence on the Isle of Mull, Scotland. 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.
Market Value Factors
Pricing varies for every rock and mineral, so use these universal factors to gauge Mullite before comparing listings or appraisals.
Size & Weight
Larger, intact specimens usually command higher prices.
Rarity & Demand
Scarce material or popular varieties sell at a premium.
Condition & Finish
Chips, repairs, and heavy wear lower value; clean prep helps.
Treatment & Provenance
Untreated specimens with documented locality are prized.
Mullite Localities Map
See where Mullite is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.
Quick Facts
Physical Properties
- Color
- Colourless, white, yellow, pink, red, gray
- Hardness (Mohs)
- 6 - 7
- Density
- 3.17 g/cm³
Chemical Properties
- Chemical Formula
- Al4+2xSi2-2xO10-x (x ~ 0.4)
- Elements
- Al, O, Si
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Mullite FAQs
How do I identify Mullite?
Mullite can be identified by its hardness of 6 - 7 on the Mohs scale, Colourless color. Look for these key characteristics when examining specimens.
What color is Mullite?
Mullite typically appears in Colourless, white, yellow, pink, red, gray. Color can vary depending on impurities and formation conditions.
How hard is Mullite?
Mullite has a hardness of 6 - 7 on the Mohs scale. This gives it moderate hardness.
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