The word 沙子 is formed through a common Chinese morphological process where the meaningful root character 沙 (shā), which denotes the concept of "sand" or "gritty particles", is combined with the suffix 子 (zi). This suffix 子 often attaches to nouns, not to change the core meaning, but to form a standard, concrete, or freestanding nominal unit. In this case, it transforms the root 沙 into the everyday, discrete noun "sand", in a way that feels complete and natural to the native speaker, similar to how "-ness" or "-er" can form nouns in English.