Wollastonite, also silanized

Wollastonite is a natural fibrous calcium silicate (CaSiO3), which is used for reinforcement of composite materials, such as e.g. friction materials, ceramics, plastics and paints. It also helps to modify the friction level of brake pads and linings. 

Wollastonite is insoluble in water, diluted acids as well as hot concentrated sulfuric acid, and offers a high thermal stability. Compared with other fillers it has a relatively high hardness on the Mohs scale (4.5-5) and - depending on the purity - a density between 2.8g/cm3-3.1g/cm3.