schistaceous

adjective2

1. •
   Containing schist or exhibiting schistosity; schistose.

   • Wills does not just climb cliffs or scramble over boulders; he negotiates "schistaceous gneiss." — 1999
2. •
   Having the color of slate; slaty

   • Eyes golden-green. Mouth black. Thorax schistaceous beneath. — 1851