Final answer:
Limestone can be a heterogeneous mixture with impurities or in pure form, a compound of calcium carbonate (CaCO3). Its classification as a mixture or pure substance depends on the purity of the sample.
Step-by-step explanation:
Limestone is commonly classified as a mix-ture, specifically a heterogeneous mixture, as it often contains various impurities such as sand and clay particles, fossil fragments, and different minerals. However, it primarily consists of calcium carbonate (CaCO3), which in its purest form is a pure substance and a compound. A pure substance has a constant composition and set properties, such as a single melting point and single boiling point.
When considering mixtures, these are combinations of two or more substances, where each retains its individual properties. Limestone can come in different qualities, with varying proportions of impurities, which affects its overall composition and properties. Therefore, its classification may depend on the context and purity of the sample being considered.