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FORMATION OF QUARTZ OVERGROWTHS IN THE PENRITH SANDSTONE (LOWER PERMIAN) OF NORTHWEST ENGLAND AS REVEALED BY SCANNING ELECTRON MICROSCOPY
Author(s) -
WAUGH B.
Publication year - 1970
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1970.tb00197.x
Subject(s) - quartz , geology , crystallite , scanning electron microscope , orientation (vector space) , crystallography , prism , mineralogy , crystal (programming language) , permian , geometry , materials science , paleontology , optics , composite material , structural basin , chemistry , programming language , mathematics , computer science , physics
SUMMARY The development of optically continuous quartz overgrowths is governed by the atomic structure and crystallographic orientation of the detrital quartz grains. Initial growth commences with the appearance of numerous oriented projections, with rhombohedral and prismatic form, on grain surfaces. Merging and overlap of the projections results in the formation of large crystal faces whose form is dependent upon the initial location of the projections with respect to the internal crystallographic axes. Growth is particularly rapid along the direction of the c‐axis. For unicrystalline quartz grains the ultimate growth phase is the production of polyhedral quartz crystals having the appearance of hexagonal dipyramids. In polycrystalline grains each quartz unit within a single grain develops a separate overgrowth, the form of which is similarly controlled by the internal structure of the individual quartz units. Hence, the completed overgrowth shows an irregular distribution of diversely oriented prism and rhombohedral faces.