The Crystalline Quartz-rich Raw Material from Olduvai Gorge (Tanzania): Why is it called quartzite when it should be called quartz?

Abstract

Abstract The major raw material documented in the archaeological sites of Olduvai Gorge (Tanzania) is a geological material with crystalline appearance, white or colorless, foliated or seemingly massive only at the outcrop scale, with a very high quartz-rich composition, and apparently bearing a metamorphic origin (CQRM). Since the early days of research in Olduvai Gorge, a long-lasting terminological imprecision has allowed defining this material in a confused way as quartz or quartzite. Stubbornness in terminological imprecision reflects the complexity and specificity of CQRM related to a protracted and complex geological history composed by quartz-bearing metamorphic rocks of varied types and origins from recycling and/or tectonic reworking of much older Precambrian orogens and cratons. Currently the term quartzite is preferred by most researchers, despite being materials that have an appearance macro and microscopic similar to quartz and show a response to fracture mechanics and cutting-edge functional response is closer to quartz. In our view it is crucial to undertake a comprehensive analysis of the CQRM from the structural, metamorphic and petrological perspectives. Bearing this in mind, the main objective of the present study is to build a robust and conclusive background that will enable an accurate identification and classification of this quartz-rich mineral resource. This geological material should be identified as “Quartz” and he most diagnostic features supporting this interpretation can be summarized as: some of the microstructural relics identified concur undoubtedly with a hydrothermal origin, and the recognition of special deformational structures/microstructures point to tectono-metamorphic processes under granulite-facies conditions.