firestone: a sandstone that withstands intense heat; used to line fireplaces and furnaces and kilns
sandstone: a sedimentary rock consisting of sand consolidated with some cement (clay or quartz etc.)
cartesian coordinate: one of the coordinates in a system of coordinates that locates a point on a plane or in space by its distance from two lines or three planes respectively; the two lines or the intersections of the three planes are the coordinate axes