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. Biotite granite is a coarse grained, felsic intrusive rock, the minerals which make up a granite are typically quartz, feldspars and micas. In the case of biotite granite, the constituent minerals are milky (white) quartz, plagioclase feldspar which is often white and biotite mica crystals. Approx: 30-40mm
