Petrography

About: Petrography is a research topic. Over the lifetime, 7449 publications have been published within this topic receiving 102018 citations.

Petrographic and engineering properties of sandstones from the Sneinton Formation, Nottinghamshire, England

Abstract: The Sneinton Formation occurs at the base of the Mercia Mudstone Group and consists of sandstones with interbedded siltstones and mudstones. The sample material was obtained from core from a 63 m deep borehole sunk near Epperstone some 10 km north of Nottingham. The petrographic characteristics, namely quartz content, clay size content, packing density and particle size distribution of the sandstones, were determined for a series of depths. In addition, the density, porosity, compressive and indirect tensile strengths, hardness, modulus of deformation, Poisson9s ratio and slake durability index were determined for the same depth intervals. The petrographic characteristics then were correlated with the physical and mechanical properties and the significance of the relationships assessed by Student9s t value. The individual physical and mechanical properties also were the correlated with each other and the significance of the relationships similarly assessed.

The influence of the characteristics of quartz and mineral deterioration on the strength of granitic dimensional stones

Abstract: It is important to have a thorough knowledge of the petrographic characteristics of rocks to evaluate and understand their mechanical behavior. This paper deals with the influence of the texture and the mineral characteristics of nine Portuguese granites employed as dimensional stones. This study evaluates different mineral characteristics, such as mineral deterioration, grain size, quartz fissuration and the contacts between quartz and others mineral groups. The main differences in the studied granites were identified, clarifying the relationship between the petrographic characteristics. The consequences on their respective mechanical behavior were subsequently evaluated. The physical and textural characteristics of quartz in the studied granites have proven to be very important for understanding the behavior of granitic rocks under compressive stress. Uniaxial compressive strength values are not proportional to the quartz–feldspar ratio or quartz content and there is a tendency for strength to decrease with the increase in quartz. This could be related to the increase in quartz-quartz contacts and the decrease in the rock capacity for accommodating the deformation.

Alteration and Fluid Inclusion Studies of the Porphyry Copper Ore Body at Bingham, Utah

Abstract: Distribution patterns for biotitic alteration, sericitic alteration, and distinctive fluid-inclusion types in igneous host rocks of the porphyry copper ore body at Bingham, Utah, have been determined by petrographic examination of about 300 samples. These patterns are related to differences in original rock composition, variations in physical-chemical conditions during periods of intrusion and mineralization, and spatial position within the ore body.The distribution of biotitic (potassium-silicate) alteration assemblages and high-salinity fluid inclusions generally follows the crudely triangular form of the disseminated copper ore zone. Variations in abundance of hydrothermal biotite are attributed to differences in original mafic mineral content of the igneous host rocks. Biotitic alteration and initial copper mineralization were accomplished by high-salinity fluids concentrated during final crystallization of the monzonitic parent magma; genetic continuity between magmatic and hydrothermal stages is indicated.Pervasive sericitic alteration of plagioclase is confined to rocks in the northern one-third of the Bingham stock; a subzone of argillic alteration in the north-central part of the ore body occurs within the broader area of sericitic alteration. Fluids responsible for sericitic and argillic alteration were channeled by a broad zone of northeast-trending fractures.Hydrothermal minerals and high-salinity fluid inclusions occur within a large volume of shattered rock. Boiling of fluids during crystallization of the aplitic porphyry may account for the shattering. Sericitic (and argillic) alteration were apparently super-imposed on the earlier biotitic assemblage as the hydrothermal system cooled. Cooling and hydrolytic alteration were promoted by progressive introduction of meteoric waters. The many generations of inclusions trapped from boiling fluids in the temperature range 400 degrees to 600 degrees C suggest that the system was recharged repeatedly during the period of mineralization. Estimated fluid pressures of about 800 bars in the early stages of mineralization correspond to a lithostatic load of about 3 km; pressures were even lower (less than 200 bars) in the later stages and were probably controlled by hydrostatic conditions.

A Color Guide to the Petrography of Sandstones, Siltstones, Shales and Associated Rocks

Abstract: AAPG Memoir 109 is designed as a practical guide for students and professionals to learn the fundamentals of microscopic examination of sandstones, mudrocks, and associated rocks. With more than 1100 color illustrations, it covers the identification of grains, textures, and structures of clastic terrigenous rocks as well as their diagenetic alteration (compaction, cementation, dissolution, and replacement) and porosity reduction or enhancement. It also provides classification diagrams for formal description of those rocks and their porosity. Although the majority of the outcrop and subsurface examples come from the United States (35 states and Puerto Rico), there are representative photographs from 32 other countries, including many from the offshore areas. The foldout birefringence chart and an included DVD with Powerpoint files of all of the petrographic images provide additional aids for instructors and students.