The Impact of Mineralogical Characteristics on the Physicomechanical Properties of Serpentinite from Prang Ghar, Mohmand District, Pakistan

Abstract

The serpentinite samples of the Prang Ghar Mohmand Agency were analysed petrographically and physicomechanically to assess their potential as dimension stone and aggregate material. These rocks are prominently exposed along the suture zone between the Indian Plate and the Kohistan Island Arc, known as the Main Mantle Thrust Zone (MMTZ).  On fresh surfaces, the serpentinite ranges in color from light green to dark green, while weathered surfaces appear yellowish green. Petrographically, the serpentinite is fine- to medium-grained and consists of serpentine, actinolite, talc, and magnesite, along with ore minerals like magnetite and chromite in varying amounts. The serpentinite can be categorized into four types: serpentinite, talc-serpentinite, actinolite-serpentinite, and chromite-bearing serpentinite. The physicomechanical properties were assessed through a series of tests, which were then compared to ASTM standards to evaluate their quality. These tests included unconfined compressive strength (UCS) (46.0–49.94 MPa), cube test (198.56–234.34 MPa), flexural test (8.20–13.28 MPa), specific gravity (2.58 mg/cm³), and soundness (3.35%). The results indicate that the serpentinite exhibits properties that meet international standards for use as dimension stone and coarse aggregate. Based on these findings, it can be concluded that the Prang Ghar serpentinite is a viable material for construction applications, such as flooring and exterior wall cladding. This study emphasizes the strong correlation between the mineral composition of serpentinite and their physicomechanical properties. An increase in talc content is associated with reduced strength, along with higher water absorption and porosity. Additionally, the presence of actinolite and ore minerals also influences the physicomechanical behavior of serpentinite. This study confirms the necessity of petrographic analysis before using rock as an engineering material.

Keywords: Dimension stone, Prang Ghar, serpentinite, petrography, physicomechanical properties.