Univrsity of Tehran Press Geopersia 2228-7817 16 1 2026 06 03 Thermal Effects on Microcracking and Physical Characteristics of Khoramdareh, Natanz, Nehbandan, and Taibad Granites - 129 152 103569 10.22059/geope.2025.390516.648809 EN Saeed Nejati Faculty of Basic Sciences, Tarbiat Modares University, Tehran, Iran Mashalah Khamehchiyan Faculty of Basic Sciences, Tarbiat Modares University, Tehran, Iran Mohammad Reza Nikudel Faculty of Basic Sciences, Tarbiat Modares University, Tehran, Iran Journal Article 2025 02 14 This study explores the thermal behavior of four widely used Iranian granites - Khoramdareh,<br />Nehbandan, Natanz, and Taibad - under temperatures ranging from 20°C to 1050°C. The investigation<br />focused on the evolution of microcracks and their impact on key physical properties such as porosity,<br />water absorption, and P-wave velocity in both dry and saturated conditions. Using fluorescence<br />microscopy, linear microcrack density (LMD), microcracks type, and width were analyzed in detail. At<br />300°C, all granite samples showed an increase in inter-crystalline microcracks, leading to elevated<br />porosity and water absorption. At 600°C, the quartz phase transition at 573°C resulted in volumetric<br />expansion, causing a temporary decrease in porosity and an increase in P wave velocity. For example,<br />the dry P wave velocities at 600°C were 4.77 km/s for Taibad, 4.71 km/s for Khoramdareh, 3.84 km/s<br />for Natanz, and 5.12 km/s for Nehbandan. Above 750°C, trans-crystalline microcracks became<br />dominant, significantly increasing porosity and water absorption while reducing P wave velocity.<br />Nehbandan granite suffered structural failure at 600°C, whereas Natanz exhibited the highest LMD at<br />750°C, indicating severe internal damage. The study highlights the importance of microcracks evolution<br />and mineralogical transformations, particularly quartz phase transitions, in controlling granite's thermal<br />stability. Three critical thresholds (300°C, 600°C, and 750°C) were identified as turning points in the<br />deterioration process. Additionally, this research introduces a novel methodological approach,<br />combining fluorescence microscopy with physical testing to achieve detailed characterization of thermal<br />damage. By extending the temperature range up to 1050°C, the study provides valuable insights into<br />granite performance in fire-prone and heat-exposed environments.<br /><br /> https://geopersia.ut.ac.ir/article_103569_4e1cd693d8603ccdab8cf995c3359b7e.pdf