Ice: http://www.agu.org/pubs/crossref/1983/JB088iB02p01197.shtml says ice has tensile strength of 17 MPa and frozen mud 21 MPa. "Pykrete" which is frozen ice where the water was mixed with 14% wood pulp or sawdust, is over 4X stronger than plain ice and also less brittle, and if you use newspapers you can make it stronger still ("super pykrete"). Rock tensile strengths http://www.finesoftware.eu/geotechnical-software/help/rock-stability/tensile... for 10 kinds of rock range from 2 to 23 MPa. Typical steel tensile strength is 250 MPa and for high strength steels can be over 1 GPa. So again, the question of whether the Tunguska object was ice or rock seems pretty irrelevant to the fracture question -- and steel is over 10X tougher than either.