SEDMIN - Microsoft Excel™ spreadsheet for calculating fine-grained sedimentary rock mineralogy from bulk geochemical analysis

Abstract

Normative mineralogical calculations from bulk geochemistry of sedimentary rocks are problematic because of variable depositional environments, particle hydraulics and sedimentary source systems. The development of SEDMIN, a Microsoft Excel™ spreadsheet solution, is a practical attempt for a computational routine focusing specifically on smectite, chlorite, kaolinite, illite and the ambiguous sericite within various pelitic sedimentary lithologies. While in essence a mathematical approach, the use of statistical evaluation of empirical lithogeochemical data combined with modal analytical procedures yields reasonable geochemical associations, more precise chemical phases and revised procedural allotment paradigms. Thus, an algorithm using TiO2 as a key to the normative calculation of kaolinite is proposed. Incorporating additional parameters, such as LOI (Loss-on-ignition) in conjunction with carbon, sulfur, carbonate and sulfate, provides that clay phases can be more accurately determined than from bulk oxides alone. Even when presented with atypical sample data, the spreadsheet solution is able to accurately predict predominant clay minerals. Besides some drawbacks, the likely benefit from SEDMIN is the incorporation of results in classification norms and diagrams indicative of sedimentary lithologies. The ”SEDMIN Sedimentary Mineral Calculator.xlsx” spreadsheet can be freely downloaded from http://earthscienceeducation.net/SEDMINSedimentaryMineralCalculator.xlsx.