Precambrian Phyllite (metamorphic conglomerate) 1,800Ma, Prescott AZ
About 1,800 million years (Ma) ago, a sedimentary conglomerate with round pebbles was subducted into an oceanic trench, transforming it into a metamorphic phyllite. During this process, the pebbles were flattened out into pancakes less than 0.5cm think and over 20cm in diameter. Seen here in cross section, they appear as thin streaks with tapered ends. Some of the larger pebbles (dark reddish at the upper left corner and at right) are still lens shaped with tapered corners. Size approx 20 by 30 cm. Prescott Heights AZ, Center for Natural History
Precambrian Phyllite (metamorphic conglomerate) 1,800Ma, Prescott AZ
About 1,800 million years (Ma) ago, a sedimentary conglomerate with round pebbles was subducted into an oceanic trench, transforming it into a metamorphic phyllite. During this process, the pebbles were flattened out into pancakes less than 0.5cm think and over 20cm in diameter. Seen here in cross section, they appear as thin streaks with tapered ends. Some of the larger pebbles (dark reddish at the upper left corner and at right) are still lens shaped with tapered corners. Size approx 20 by 30 cm. Prescott Heights AZ, Center for Natural History