![25.1 Porphyritic hornblende andesite. Mosquito Lake, California. Tiny to 3 mm aligned and elongate black phenocrysts of hornblende and a few glassy white to cream-colored, commonly rectangular, phenocrysts of plagioclase characterize the phyric grains of this rock, which has an aphanitic, dark gray groundmass. [Scale is standard GSA scale with mm diameter dots of 2 mm to 5 mm diameter.]](../25.1.JPG)
25.1 Porphyritic hornblende andesite. Mosquito Lake, California. Tiny to 3 mm aligned and elongate black phenocrysts of hornblende and a few glassy white to cream-colored, commonly rectangular, phenocrysts of plagioclase characterize the phyric grains of this rock, which has an aphanitic, dark gray groundmass. [Scale is standard GSA scale with mm diameter dots of 2 mm to 5 mm diameter.]