Mullite
Mineral Al6Si2O13
About it
Needle-like aluminium silicate formed when clay-rich rock is baked by magma, named for the Isle of Mull, Scotland; it is also the key crystal in fired porcelain and refractory brick.
- Type
- Mineral
- Group
- Silicate (nesosilicate), mullite group
- Formula
- Al6Si2O13
- Hardness (Mohs)
- 6–7
- Specific gravity
- 3.11–3.26
- Streak
- white
- Lustre
- vitreous (glassy)
- Crystal system
- Orthorhombic
- Colours
- colourless, pale pink, grey
- Transparency
- transparent, translucent
- Cleavage and fracture
- distinct in one direction
Typical values: real specimens vary. For more, see mindat.org.