Excellent activity to follow study of crystal structure, students identify minerals by physical properties of cleavage and fracture. Included are samples which show cleavage in 1, 2, 3, 4 and 6 directions, and exhibit conchoidal and uneven fracture. Students use a goniometer to study cleavage direction and relate properties of the minerals to their commercial uses. Kits contains five specimens each of: biotite mica, calcite, fluorite, halite, hornblende, microcline feldspar and sphalerite; eight specimens each of: obsidian, serpentine; 15 contact goniometers; and 30 student worksheets. Comes with teacher's instruction booklet providing full background information and materials for 30 students.