Fluvial Sand, Botswana stream
Location:
Metsimotlhabe river (Kumakwane~25 km from Gaborone), Botswana along the river bed. (Latitude
-24.69S and Longitude 25.71E).
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
quarz. 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.
Glass bead is 200µ in diameter.
Texture:
Medium-grained (mL, 250-350µ), poorly sorted, subangular-subrounded.
Sample Number:
heubeck0140
Collector:
Elisha M. Shemang, Botswana; Dept. of Geology, University of Botswana.
Date:
Friday January 11th 2008
Comments:
Mineral color in quarz 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.
