The Opal series consists of moderately deep, well drained soils formed in clayey sediments weathered from clay shale on uplands.
Permeability is very slow.
Slopes range from 0 to 25 percent. The depth to soft shale is typically 28 to 35 inches and ranges from 20 to 40 inches. The depth to carbonates ranges from 0 to 8 inches. Pebbles range from 0 to 5 percent, by volume, throughout the solum. The A horizon has hue of 10YR, 2.5Y or 5Y, value of 4 or 5 and 2 or 3 moist, and chroma of 1 or 2.