Chert
Image: <a href="//commons.wikimedia.org/wiki/User:Olga_Ernst" title="User:Olga Ernst">Olga Ernst</a> (CC BY-SA 4.0)
Mineral NameChert
Chemical FormulaSiO2
Mohs Hardness7
Crystal Systemtrigonal
Streak ColorWhite
CleavageNone
FractureConchoidal
Specific Gravity2.65
Colorswhite, grey, brown, tan, reddish-brown
TransparencyTranslucent to opaque
Type LocalityMalmani Formation, Pretoria area, South Africa
Mineral GroupSilicates
Usesflint tools, building material, aggregate, collector's item
Associated Mineralsdolomite, quartz, chalcedony
Raritycommon
Description
This image displays a large, weathered block of chert-bearing and stromatolitic dolostone, featuring layers of light tan, grey, and reddish-brown material with intricate, wavy patterns characteristic of stromatolites. The rock surface is rough and shows conspicuous traces of weathering.
Geological Context
Chert, a microcrystalline form of quartz, commonly forms in sedimentary environments, often associated with carbonates like dolomite, and can preserve ancient microbial structures such as stromatolites. This particular sample is from the Paleoproterozoic Malmani Formation, indicating its formation in ancient shallow marine settings.
