Marble Countertop Maintenance With marble, French Limestone, onyx, and other calcium based stones becoming very popular for countertops, vanities, and vertical surfaces, the need for a comprehensive maintenance program is imperative. Calcium based materials are very chemically sensitive. Of course because they are also much softer on the Mohs Hardness scale, they scratch more easily as well. Knife steel is about a 6.5 on the hardness scale and marble is between 3-4. Therefore by choosing one of...