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Classification of Tufa Rocks by Using IUGS and TAS Classification Methods Based on Visual and Petrographic Identification
Novi Asniar, Yusep Muslih Purwana, Niken Silmi Surjandari

Sebelas Maret University


Abstract

Tufa rocks are pyroclastic rocks from volcanic eruptions which are then sedimentated and subsequently undergo metamorphosis. This sedimentation and metamorphosis process causes confusion and debate in naming / classifying tufa rocks. The process of visual identification of tufa rocks in the field is based on the color and size of the pyroclastic material. Petrographic analysis was carried out to find out more about the mineral and chemical content of tuffaceous rocks so that the classification of tufa rocks could be more specific. Minerals in tufa rocks are divided into primary minerals (primary minerals) and secondary minerals (secondary minerals). Primary minerals usually number more than secondary minerals and are referred to as phenocrysts (plagioclase and quartz feldfar). Secondary minerals in the form of white mica (muscovit), chlorite, epidote / clinozoisite, albite, actinolite, titanite, pyrite, and calcite. This paper summarizes the method of identifying tufa rocks from the collection of various literature on visual identification and petrographic analysis of tufa rocks from various locations in the world including Indonesia. The classification method used is: International Union of Geological Sciences (IUGS) based on phenocrysts content (and rock color), and Total Alkalis versus Silica (TAS) based on chemical content. In general, tufa rocks from various locations in the world and Indonesia are classified as dacite or rhyodacite rocks based on IUGS classification and classified as rhyolite rocks (SiO2 = 62% - 77%) based on the TAS classification.

Keywords: classification, Tufa Rocks, visual identification, petrographic

Topic: International Symposium of Civil, Environmental, and Infrastructure Engineering

Link: https://ifory.id/abstract/MHm9Fa2urkcZ

Conference: The 3rd International Conference on Sustainability and Innovation (ICoSI 2019)

Plain Format | Corresponding Author (Novi Asniar)

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