Biggs jasper is found between two of the
basalt lava flows that once covered the U.S. states of
Oregon,
Washington and parts of
Idaho. Many thousands of years passed between the individual flows, allowing life to flourish. During this time, the volcanic ash decomposed into
clay and was deposited by rain water in streams and lakes atop the cooled basalt. There it mixed with
silica and
iron from the
weathering of the then-recent
igneous rocks, forming a plastic
colloid. When lava next flowed over it, the heat and pressure transformed the muddy mixture. As water escaped it in the form of superheated steam, pressure variations resulted in flexing and many short fluctuating changes, reflected in the jasper's many thin, parallel bands. The hydrothermal reaction progressed as a shock wave through the mud, removing iron from it and depositing the iron as intertwining bands of
limonite. The altered rock remained
plastic, and subject to local movement as a result of pressure changes. These caused the great variety of marbled,
rosette-like and picture designs found in Biggs jasper. Near Biggs jasper a
stratum of white clay is sometimes found, locally named "wascoite" for the town of
Wasco, Oregon. It is probably the end form of much-weathered volcanic debris. Also often found together with Biggs jasper is a dark gray, somewhat
translucent chert. It formed from colloidal
silica released from the volcanic debris. Because of their different physical properties, water movement separated the two colloids from which the chert and Biggs jasper resulted from each other, so that both were deposited in nearly pure form. ==Use==