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. Granite is a very hard, granular, crystalline igneous rock which consists mainly of quartz, mica, and feldspar and is often used as building stone Adamellite is a coarse-grained porphyritic igneous rock, a variety of Monzogranite and dominated by phenocrysts of orthoclase in a granular groundmass of perthite, plagioclase and quartz Approx: 30-40mm
