Sillimanite (Chemical Formula: Al2SiO5) is the alumino-silicate mineral, which shares allotropy with Kyanite and Andalusite. Sillimanite is rough, abrasive and scores 6-7 (Moh’s scale of hardness). Fibrolite is the common variety of Sillimanite and it is named after its fibrous structure when seen by the naked eye.


The volume porosity of Sillimanite grains rarely exceeds 6% after heating and it decreases further, when heated for a long time. This compactness makes it perfect for applications where abrasion and corrosion may occur. Sillimanite has many valuable properties such as low thermal conductivity (9.10 W/m/K), high specific heat capacity, bad conductor of electricity, high melting point, neutral reaction and can withstand temperatures up to 1550 o C after which it decomposes to mullite. Sillimanite is non inflammable and non-explosive, which is why it is used in production of refractory products.


Mineralogy Guaranteed (%) Typical (%)
Garnet 96.5% 97%
Chemical Analysis   Typical (%)
Al2O3 Min 57 57-58
SiO2   37-38
Fe2O3 - 0.5-0.8
TiO2 - 0.2-0.6
CaO - 0.1-0.2
MgO - 0.05-0.1
LOl - 0.5-0.7
Na2O - 0.25-0.5
K2O - L0.2-0.4
Sieve Analysis
Mesh (US)   Retention(%)
+30   Nil
+40   0-0.5
+60   2-4
+80   30-35
+100   35-40
+140   22-26
+200   1-3
-200   0-1
Note: Sillimanite is a natural product and as such slight variations in the chemical analysis and size distribution should be expected. Special contracts covering guarantees other than those specified can be negotiated.

Industrial Applications of Sillimanite

  • Sillimanite powder is mixed with high-grade China clay for manufacturing spark plugs and other high voltage insulators. 
  • Sillimanite refractories are used in industries such as ceramics, cement, glass-making, refinery and treatment, coal carbonisation, iron foundries and manufacture. 
  • Sillimanite is used as a lining material in glass melting furnace.
  • Sillimanite is fast becoming zircon replacement in smaller castings.
  • At Euromax, we offer high quality processed Sillimanite powder in bulk to meet customer specifications.

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