Tyndall stone

noun1

1. •
   (Canada) A dolomitic limestone quarried in the vicinity of Tyndall, Manitoba, Canada, famous for its pervasive mottling and numerous fossils.

   • More and more my father chooses to decorate the stone surfaces with elaborate cipher, even though Tyndall stone, with its mottled coloring, is thought to be resistant to fine carving. — 1994