Trachyte is a fine-grained, alkali-rich volcanic rock composed predominantly of alkali feldspar, with lesser amounts of mafic minerals. It is significant in petrology for understanding the evolution of alkaline magmas, the processes of magmatic differentiation, and the geochemistry of volcanic rocks.
Source Le Maitre, R. W. (2002). “Igneous Rocks: A Classification and Glossary of Terms.” Cambridge University Press.