Description All our rocks are carefully selected for educational study. Average specimen size is shown below. These are ideal for classroom teaching and are a size that can be easily passed round the classroom for students to get a feel for each type. Limestone is a carbonate sedimentary rock that is often composed of the skeletal fragments of marine organisms such as coral, foraminifera, and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate. Approx: 30-40mm
