It is possible for a knife to scratch a Valley Gold Vein Marble countertop. Marble is generally considered a softer stone compared to other countertop materials like granite, quartz, or stainless steel. Therefore, using a sharp knife directly on the surface of the marble countertop can potentially leave scratches or marks. To avoid this, it is recommended to use a cutting board or other protective surfaces when working with knives on marble countertops.