A fine, naturally occurring, lightweight silica. Tripoli is a sedimentary stone composed of diatoms and finely weathered chert. It is derived from schistose rocks. It was originally obtained from northern Africa, but is now quarried in the USA. Tripoli is used as an abrasive, as a filtering medium and as a filler in paints. Synonyms: tripolite; tripoli powder; diatomaceous earth; soft silica. Museum of Fine Arts, Boston (2000); Trench (2000). [J. Cassar, R. de Angelis]