pozzuolana

noun

1. a volcanic rock, powdered and used in making a hydraulic cement
2. a siliceous or siliceous-and-aluminous material that will, in finely divided form and in the presence of moisture, react with calcium hydroxide to form a cement

Etymology: It < L puteolana (pulvie), (powder of) Puteoli (now It Pozzuoli), site of the quarries