A mineral, usually used in a powdered form. Talc is used to prevent malignant pleural effusions from coming back. Malignant pleural effusion is a condition in which cancer causes an abnormal collection of fluid in the space between the lung and chest wall. When talc is inserted into the pleural space, it causes the space to close up so fluid cannot collect there. Also called Sclerosol Intrapleural Aerosol, sterile talc powder, and Steritalc.