Abstract: A composition of matter is disclosed which includes rubber, plastomer and elastomer materials, that is, natural and synthetic rubbers and polymeric materials commonly referred to as plastics containing as a filler material a carbonaceous siliceous material derived from organic agricultural material having high initial silica contents (for example, rice hulls) of up to about 28%; which carbonaceous siliceous material is obtained from the original organic agricultural material by a process of controlled incineration such that the resulting material contains minor residual impurities and small quantities of residual carbon and is amorphous in nature while retaining the original cellular structure of the agricultural material from which it is derived; the rubber; elastomeric and plastomeric compositions also may contain other ordinary components used in the preparation of such materials employing other fillers.