Quartzite is a metamorphic rock made almost entirely of quartz (SiO₂), formed when sandstone is subjected to extreme heat and pressure deep in the earth's crust. The quartz grains fuse together into an interlocking crystalline mass — far harder and denser than the original sand. Marble, by contrast, is metamorphosed limestone and made of calcite (CaCO₃). The practical difference is dramatic: quartzite scores 7 on the Mohs hardness scale versus marble's 3, making it resistant to scratching, etching, and acid damage. It will not react with lemon juice, vinegar, or wine. For clients who love the veined look of natural stone but need kitchen-proof durability, quartzite is the answer.