WoldWide Drilling Resource

Frequently-Used Geological Terms Part 83 Glossary Adapted from the Dictionary of Geological Terms R Richter Scale - A numerical scale of earthquake magnitude. It was created in 1935, by seismologist C.F. Richter. Very small, or microearthquakes can have negative magnitude values. In theory, there is no upper limit to the magnitude of an earthquake, but the strength of earth materials produces an actual upper limit of slightly less than 9. Riebeckite - A blue or black monoclinic mineral of the amphibole group. It occurs as a primary constituent in some acid- or sodium-rich igneous rocks. Rigidity - The property of a material to resist applied stress that would tend to distort it. Fluids have zero rigidity. Rimrock - An outcrop of a horizontal layer of resistant rock, such as a lava flow at the edge of a plateau or mesa. It typically forms a cliff or ledge. Could also be used to describe the bedrock forming or rising above the margin of a placer deposit. Riprap - Large fragments of broken rock, thrown together irregularly or fitted together. Its purpose is to prevent erosion by waves or currents and thereby preserve a surface, slope, or underlying structure. It is used for irrigation channels, river improvement, spillways at dams, and seawalls for shore protection. Road Metal - Crushed and graded stone used in the foundation or base course of paved highways. Rock - An aggregate of one or more minerals such as granite, shale, and marble. Or a body of undifferentiated mineral matter like obsidian. Solid organic material such as coal is also re- ferred to as a rock. Rock Bolting - A method of securing or strengthening rocks in mine workings, tunnels, or rock abutments by inserting and firmly anchoring rock bolts in predrilled holes. A device on the leading end expands when the bolts are tightened. Rock Burst - A sudden and often violent breaking of a mass of rock from the walls of a tunnel, mine, or deep quarry, caused by the release of accumulated strain energy. It may result in closure of a mine opening, or projection of broken rock into it, accompanied by ground tremors, rockfalls, and air concussions. Look for more terms next month! Riprap. C&G 22 JULY 2019 WorldWide Drilling Resource ®