The Collaborative International Dictionary
Polymnite
Polymnite \Pol"ym*nite\, n. [Gr. ? full of moss; poly`s much + ? moss.] (Min.) A stone marked with dendrites and black lines, and so disposed as to represent rivers, marshes, etc.
Wiktionary
polymnite
n. (context mineralogy English) A stone marked with dendrites and black lines, and so disposed as to represent rivers, marshes, etc.