Fluvial Sand, Botswana stream
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Metsimotlhabe river |
Glass bead is 200µ in diameter |
Location |
Metsimotlhabe river (Kumakwane~25 km from Gaborone), Botswana along the river bed. (Latitude -24.69S and Longitude 25.71E) |
Depositional facies |
River bed |
Provenance |
The river flows through waterberg group of rocks, which are an assemblage of sandstones, conglomerates and siltstones. This is continental red bed sediments |
Composition |
Predominantly coarse grained quartz with a few grains of chert and rock fragments, dominant typically blocky, equant, translucent and milky-white, rarely yellowish monocrystalline quartz. Rare transparent clear quartz crystals; trace quantitites of epidote, rutile, zircon, sphene and possibly garnet. Most grains are coated with an FeOx cutane. FeOx minerals (goethite ?) precipitated repeatedly from groundwater after sand was occasionally moistened and capillary water evaporated |
Texture |
Medium-grained (mL, 250-350µ), poorly sorted, subangular-subrounded |
Petrographic thin section:
Description |
insert here short description of thin section |
insert here a bright field image |
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insert here a dark field image |
Bright field |
Dark field |
Sample number |
heubeck0140 |
Collector |
Elisha M. Shemang, Dept. of Geology, University of Botswana |
Date of sampling |
11.01.2008 |
Comments:
Mineral color in quartz is due to impurities of rutile, tourmaline or Fe-oxides intergrown with the quartz crystal. Additionally, gas and liquid bubbles trapped during crystallization reduce transparency
