set of various dark unpolished stones on

aegirine anthracite background basalt bituminous black bornite chromite coal collage collection cutout description flint flintstone gabbro gemstone glass gneiss hematite hyalobasalt ilmenite iron isolated kidney lodestone magnetite many marmatite mineral molybdenite name natural nepheline obsidian ore perovskite raw rock rough set shale shungite sphalerite spinel stone syenite unpolished various volcanic white