polymnite

Century Dictionary and Cyclopedia

1. n. A stone marked with dendrites and black lines, and so disposed as to represent rivers, marshes, and ponds.

Wiktionary

1. n. mineralogy A stone marked with dendrites and black lines, and so disposed as to represent rivers, marshes, etc.

GNU Webster's 1913

1. n. (Min.) A stone marked with dendrites and black lines, and so disposed as to represent rivers, marshes, etc.