All our rocks are carefully selected for educational study. They come in labelled trays. The trays are normally 3″ x 2″ size depending on the rarity of the specimen. 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.
Andesite is an extrusive volcanic rock of intermediate composition. In a general sense, it is the intermediate type between basalt and rhyolite. It is fine-grained to porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende.