ˌmärgəˈrōs ə nˌīt noun
( -s )
Etymology: Greek margaro n pearl + san is board + English -ite; from its pearly luster and lamellar structure; probably akin to Greek sathē penis, sainein to wag the tail, Old English thūma thumb — more at thumb
: a mineral PbCa 2 (SiO 3 ) 3 consisting of a lead calcium silicate occurring in colorless lamellar masses