Description Granite is a very hard, granular, crystalline igneous rock which consists mainly of quartz, mica, and feldspar and is often used as building stone Orthoclase is a feldspar mineral with a chemical composition of KAlSi3O8. It is one of the most abundant rock-forming minerals of the continental crust. Orthoclase is most widely known as the Pink Feldspar found in many granites and as the mineral assigned a hardness of “6” in the Mohs hardness scale. 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. Approx: 30-80mm
