Bytownite basalt thin section slide exhibiting phenocryts of bytownite feldspar within a fine basaltic groundmass. Bytownite feldspar is a calcium rich member of the Plagioclase family and frequently occurs as phenocrysts in mafic igneous rocks. Phenocrysts are usually euhedral in form due to early growth within the magma. Rocks containing phenocrysts represent two stages of cooling; an initial stage of cooling deep within the earths crust results in the slow formation of the large phenocrysts. This then follows by a stage of rapid cooling as the magma erupts from a volcano. These thin sections depict beautifully a textbook porphyritic texture. Each section is made to 30 microns thickness and the glass is 46 x 27 mm in size with a cover slip. Supplied in a protective card sleeve with a label, ideal for microscopy and educational purposes.