Alpedrete Granite (IMAGE) Spanish Foundation for Science and Technology Caption Alpedrete granite seen under a petrographic microscope. The main minerals are indicated: quartz (Qz), potassium feldspar (K-Fsp), plagioclase (Pl) and biotite (Bt). Credit D. M. Freire-Lista/IGEO (CSIC-UCM) Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.