Mullite

Classification:

Mullite is related to andalusite and belongs to the silicates. It has the composition Al₂SiO₅ . Chemically indentical forms in different environmental conditions are: kyanite (at high pressure), mullite (at high temperature), and sillimanite (at high pressure and high temperature). These different physical conditions induce structures, which display differences in the linkage between the aluminum and oxygen atoms: Andalusite: Al(6)Al(5)(SiO₅); Sillimanite: Al(6)Al(4)(SiO₅); Kyanite: Al(6)Al(6)(SiO₅); Mullite: Al(6)Al(4)(SiO₅) .

Synonyms/Trade Names:

Andalusite.

Chemistry/Composition:

Al₂SiO₅ . It can contain small compartments of OH and F instead of O and Fe (< 6% Fe₂O₃), and Ti instead of Al.

Structure:

The structure is related to that of sillimanite. It is created by chains of aluminum octahedra, which are linked by chains containing to 50% silicon tetrahedra and up to 50% aluminum octahedra. The size of the unit cell of mullite is slightly larger than that of sillimanite. It is suggested that mullite is a disordered phase placed between the two ordered phases sillimanite and andalusite.

Crystallographic Constants:

7.550 7.690 2.880 90.000 90.000 90.000.

Crystal Group:

Orthorhombic.

Color:

Varies from colorless to pink, white or yellow.

Optical Properties:

nx=1.639-1.661 ny=1.641-1.665 nz=1.653-1.682.

Pleochroism:

In thin section colorless and without Pleochroism.

Powder Diagram:

3.39 3.43 2.21 5.39 (15-776).

Natural Sources:

Great Britain (Isle of Mull/ Scotland).

Medical Importance:

Key Hazards:

Possibly fibrogenic.

Involved Organs:

Lung.

Exposure/Epidemiology:

It is used in ceramics and is also found in ashes of alumosilicates.

Thresholds:

In Germany, MAK 6 mg/m3.

Etiology/Pathophysiology:

Detailed data are not known.

Lung Diseases:

An aluminosis-like pneumoconiosis has been described, for further information see under the heading aluminum.

Clinical Presentation:

Associated specific symptoms are not known.

Radiology:

Associated specific findings are not known.

Lung Function:

Usually normal findings.

Bronchoalveolar Lavage:

Usually normal findings.

Pathology:

Gross:

The lungs are of normal color and consistency.

Histology:

The alveoli can contain an increased number of macrophages, and collections of brown dust particles may be seen in the lymphatic tissue.

Prognosis:

Usually good and without serious sequelae.

Additional Diseases:

None.

References:

search Pubmed for Mullite

Janko M, Mcree RE, McDonnell JF, Austria RJ: Occupational exposure and analysis of microcrystalline crystobalite in mullite operations. Am Ind Hyg Ass J 9 (1989) 460-465
Konietzko J, Dupuis H: Handbuch der Arbeitsmedizin. Ecomed, Landsberg (1990)
Stephens M, Gibbs AR, Pooley FD, Wagner JC: Asbestos induced pleural fibrosis: Pathology and mineralogy. Thorax 8 (1987) 583-588
Wagner JC, Newhouse ML, Corrin B, Rossiter CE, Griffiths DM: Correlation between lung fibre content and disease in East London asbestos factory workers. IARC Sci Publ 8 (1989) 444-448