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VOLCANIC QUARTZ AS INDICATOR MINERAL IN GRAYWACKES
Author(s) -
REIMER THOMAS O.
Publication year - 1971
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.1365-3091.1971.tb01138.x
Subject(s) - geology , quartz , precambrian , volcano , extinction (optical mineralogy) , lava , mineralogy , grain size , volcanic rock , geochemistry , mineral , sequence (biology) , paleontology , geomorphology , materials science , biology , metallurgy , genetics
Samples from an uninterrupted sequence of Early Precambrian graywackes were investigated in order to disclose whether the amount of “volcanic” quartz, i.e., quartz without undulatory extinction, can give indications of quantitative changes in the composition of the source area. As non‐undulatory quartz usually is enriched in the smaller‐size fractions, only grains with an above average grain size were considered. The minimum grain size was fixed at 0.1 mm. In each thin section 100 grains were counted and separated into two groups, one without and one with undulatory extinction. Their relation to each other was then determined and plotted in a stratigraphic column. In the same column the relation of porphyry and tuff fragments to lava fragments was plotted. The resulting similarity of the two curves shows that the quartz ratio, as introduced here, can give indications about changes in the source area of graywackes.