On weathering understanding and its characterization by petrographic indices: a study case about the criterion establishment for the textural classification of rock-forming minerals under weathering

• Published in: Environmental earth sciences 2021-06, Vol.80 (11), Article 408
• Main Authors: Monticelli, João Paulo, Sígolo, Joel Barbujiani, Futai, Marcos M.
• Format: Article
• Language: English
• Subjects: Biogeosciences; Classification; Coefficients; Criteria; Earth and Environmental Science; Earth Sciences; Engineering geology; Environmental Science and Engineering; Geochemistry; Geology; Hydrology/Water Resources; Mechanical properties; Minerals; Original Article; Rocks; Terrestrial Pollution; Weathering
• ISSN: 1866-6280; 1866-6299
• DOI: 10.1007/s12665-021-09687-3

Several studies have addressed the elaboration of petrographic indices, applicability, and their execution in the characterization of weathering grades. Petrographic indices directly depend on a visual criterion used to distinguish fresh mineral from weathered mineral, which is usually not shown. As investigated, this causes a lack of coherence among petrographic indices data for mechanical properties estimation aiming at engineering geology applications. This paper involved a readjustment of technique for the calculation of weathering indices and the establishment of criteria to gather the minerals under weathering into the petrographic index's formula based on a standardized classification of textural and micromorphological modifications. The results have shown that varying the criteria influence indices values for the same physical–mechanical properties, resulting in different types of best-fit lines, but with reasonable coefficients of determination along the weathering grades. This in part explains the variability of literature correlations. The use of a standardized classification of rock-forming minerals contributed to finding closely related mechanical degradation tendencies among literature data.