![5.1 Weathered, porphyritic quartz monzonite. Castle Crags, California. Gray glassy quartz forms square-appearing euhedral crystals that project above the surface along with the more dominant, euhedral, pink alkali feldspar crystals. Plagioclase feldspar occurs as smaller white crystals. Black bumpy spots are lichens growing on the weathered surface. [Scale is standard GSA scale with cm divisions.]](../5.1.JPG)
5.1 Weathered, porphyritic quartz monzonite. Castle Crags, California. Gray glassy quartz forms square-appearing euhedral crystals that project above the surface along with the more dominant, euhedral, pink alkali feldspar crystals. Plagioclase feldspar occurs as smaller white crystals. Black bumpy spots are lichens growing on the weathered surface. [Scale is standard GSA scale with cm divisions.]