WorldWide Drilling Resource

Frequently-Used Geological Terms Part 71 Glossary Adapted from the Dictionary of Geological Terms P Primary Mineral - A mineral formed at the same time as the surrounding rock by igneous, hydrothermal, or pneumatolytic processes which retains its original composition and form. Primary Porosity - Porosity developed during the final stages of sedimentation or which was present within sedimentary par- ticles at the time of deposition. Prime Meridian - An arbitrary line of longitude selected as a reference line having a longitude of zero degrees and used as the origin from which other longitudes are reckoned east and west to 180 degrees. Primeval - Pertaining to the earliest ages of the earth. Also said of lead (Pb) with so little uranium, such as meteorites, that the Pb-isotope composition has not changed much in five billion years. Principal Axes of Strain - Three mutually perpendicular axes corresponding to the three axes of a body which were also mutually perpendicular before deforma- tion; also described as the axes of the strain ellipsoid. The longest is the axis of elongation, and the shortest is the axis of shortening. Principal Axes of Stress - Three mutually perpendicular axes which are perpen- dicular to the principal planes of stress. Principal Axis - The crystallographic axis which is most prominent. In the tetrag- onal and hexagonal systems, it is the vertical axis. In experimental structural geology (the study of three-di- mensional distribution of large bodies of rock, as well as the composition of the inside to learn about their tectonic history, past geological environments, and events which could have changed or deformed them), it is one of the principal axes of stress or strain. Probable Ore - Refers to ore which has not been proven by development. Also refers to a mineral deposit adjacent to developed ore, which has not been proven. Probe - Any instrument placed in the environment to be measured. Producer - A producing well. Look for more terms next month! WWDR diagram. 30 MAY 2018 WorldWide Drilling Resource ®