WorldWide Drilling Resource

Frequently-Used Geological Terms Part 56 Glossary Adapted from the Dictionary of Geological Terms N Nephrite - An exceptionally tough, compact, fine-grained, greenish or bluish tremolite or actinolite, constituting the less rare kind of jade. Nested - Term used to describe volcanic cones, craters, or calderas occurring one with the other. Also said of two or more intersecting calderas. Net - In structural petrology, a stereographic or equal area projection of a sphere in which the network of meridians and parallels forms a coordinate system. It is used to plot points representing lineations, the normals to foliation, or crystallographic directions. Also refers to a series of surveying or gravity stations interconnected in such a way that closed loops of circuits are formed or so arranged as to provide a check on the consistency of the measured values. Nickeline - A pale copper-red hexagonal mineral. It is one of the chief ores of nickel and may contain antimony, cobalt, iron, and sulfur. Nonmetal - A naturally occurring sub- stance without metallic properties such as high luster, conductivity, opaqueness, and ductility. In economic geology, the term is used to define any rock or mineral mined for its nonmetallic value, such as stone, sulfur, or salt. Nontronite - An iron-rich mineral of the smectite group. Norite - A course-grained plutonic rock containing labradorite as the chief con- stituent and differing from gabbro by the presence of hypersthene as the domi- nant mafic mineral. Novaculite - A dense, hard, even-textured, and light-colored cryptocrystalline siliceous sedimentary rock, similar to chert but for the dominance of microcrystalline quartz over chalcedony. Nucleation - The beginning of crystal growth at one or more points. Nugget - A waterworn lump of placer gold or other metal. Nummulite - Any foraminifer (single- celled planktonic animal) belonging to the Nummulitidae family, characterized by a planispiral coin or lens-shaped test. Nummulitic Limestone - A sedimentary rock composed chiefly of nummulite shells. It is a thick, distinctive stone, widely dis- tributed throughout the Eocene Formation stretching from the Alps and northern Africa to China and eastern and southern Asia. Look for more terms next month! '*%+! - -! -!+ !&& +%&&!+, ,,) % -%)( ((. & !!-%(# (. +1 )+ ')+! %(")+' -%)( /%,%- ., )(&%(! 000 (10!&& +%&&!+ )+# (. +1 -$ ! (. +1 -$ ! ! " ! $ ! # $ ! !% " ! ! % ! % ! " ! " ! .+(%(# -)(! !,)+- ,%() !+)( Nickeline from Morocco, Museum des Sciences Naturelles in Brussels, Belgium. 27 WorldWide Drilling Resource ® DECEMBER 2016