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Frequently-Used Geological Terms Part 79 Glossary Adapted from the Dictionary of Geological Terms R Red Clay - A pelagic deposit which is fine-grained and reddish brown or chocolate colored, formed by the slow accumulation of material a long distance from the continents, and at depths generally greater than 11,480 feet. It contains relatively large proportions of windblown particles, meteoric and volcanic dust, pumice, shark teeth, whale ear bones, manganese nodules, and debris rafted by ice. Red Mud - A type of marine mud which is land derived and contains as much as 25% calcium carbonate. Its color is due to the presence of ferric oxide (hematite). Also refers to the residue in waste ponds and pits from bauxite processing for aluminum production. Red Ocher - A red earthy hematite, used as a pigment. Reduction Index - The rate of wear of a sedimentary particle subject to abrasion in the course of trans- portation. Reduzates - Sediments accumulated under reducing conditions and characteristically rich in organic car- bon and iron sulphide; coal and black shale are primary examples. Reflected Wave - A seismic wave which has been reflected at an interface between media with different elastic properties. Refraction - The deflection of a ray of light or of an energy wave (such as a seismic wave) due to its pas- sage from one medium to another of differing density, which changes its velocity. Refractometer - An apparatus for determining the index of refraction of a substance, either solid or liquid. Refractory Ore - Ore which is difficult to treat for recovery of the valuable substances. Regenerated Crystal - A large crystal which has grown in a mass of crushed material such as mylonite. Regolith - The fragmental and unconsolidated rock material, whether residual or transported, which nearly everywhere forms the surface of the land and overlies the bedrock. It includes rock debris of all kinds, such as volcanic ash, glacial drift, alluvium, loess, vegetal accumulations, and soil. Look for more terms next month! Red clay G&O 50 MARCH 2019 WorldWide Drilling Resource ®