WorldWide Drilling Resource

Frequently-Used Geological Terms Part 70 Glossary Adapted from the Dictionary of Geological Terms P Potassic - Said of a rock or mineral containing a significant amount of potassium. Potassium Bentonite - A potassium-bearing clay of the illite group, formed by alteration of volcanic ash. Potassium Feldspar - Any of several varieties of alkali feldspar, including sanidine, orthoclase, microcline, and adularia, that contain a high proportion of potassium relative to sodium. Also called K-feldspar. Potential Ore - Undiscovered mineral deposits, or a known mineral deposit for which recovery is not economically feasible. Also known as possibly ore, inferred ore, or indicated ore. Potentiometer - An electrical instrument for the precise measurement of low-level direct-current voltages. Potter’s Clay - A plastic clay free from iron and devoid of fissility, suitable for modeling or making of pottery or adapted for use on a potter’s wheel. It is white after firing. Pozzolan - Siliceous material such as diatomaceous earth, opaline chert, and certain tuffs, which can be finely ground and combined with portland cement. The pozzolan re- acts with calcium hydroxide which is liberated as concrete hardens, forming compounds with cementitious properties. Pozzolans also counteract the adverse effects of certain undesirable aggregates which may have to be used in concrete. Portland-pozzolan ce- ments are highly resistant to penetration and corrosion by saltwater. The name comes from the town of Pozzuoli, Italy, near which occurs a leucite tuff which was used in cement in Roman times. Precambrian - All geologic time, and its corresponding rocks, before the beginning of the Paleozoic. It is equiva- lent to about 90% of geologic time. Precious Metal - Gold, silver, or any of the minerals of the platinum group. Precious Stone - A relatively rare, durable gemstone of unusual beauty such as diamond, ruby, emerald, and sapphire. Pressure Head - The height of a column of liquid supported, or capable of being supported, by pressure at a point in the liquid. The height a column of water rises in a tightly-cased well. The pressure head is commonly expressed with reference to the land surface at the well or to some other convenient level. Look for more terms next month! Photo of Pozzolan deposits in Southern California by Dr. Vladimir Ronin. 48 MARCH 2018 WorldWide Drilling Resource ®