plane {
   -z, 0
   texture {
      tiles {
         texture {
            pigment {
               marble
               color_map {
                  [0.0 color rgb <1, 1, 1>]
                  [0.75 color rgb <0.75, 0.75, 0.75>]
                  [1.0 color rgb <0, 0, 0>]
               }
               turbulence 0.8
            }
            finish { phong 0.7 }
         }
         tile2
         texture {
            pigment {
               marble
               color_map {
                  [0.0 color rgb <0, 0, 0>]
                  [0.75 color rgb <0.25, 0.25, 0.25>]
                  [1.0 color rgb <1, 1, 1>]
               }
               turbulence 0.8
            }
            finish { phong 0.7 }
            rotate <0, 0, 90>
         }
      }
   }
}

light_source { <5, 0, -6> color rgb <1, 1, 1> }

camera {
   location <0, 0, -6>
   look_at <0, 0, 0>
}