Issue 74

N. Meddour et alii, Fracture and Structural Integrity, 74 (2025) 227-261; DOI: 10.3221/IGF-ESIS.74.16

feldspar, quartz, chlorite and muscovite (Fig. 8b), photomicrograph of thin section 04 showing fossils under cross polarized light at 6.3x magnification). The cement covers around 40% of the total volume of the rock and takes the form of a microspartic composed of calcite averaging 0.05 mm in size (Fig. 8c), photomicrograph of thin section 04 showing Muscovite under cross-polarized light at 10x magnification).

Muscovite

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(b) (c) Figure 7: Petrographic study of thin section for sample PE1-5 (T1).

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(d) Figure 8: Petrographic study of thin section for sample PE2-6 (T6).

Fossils are widespread in the rock, showing various forms of nummulites, radiolarians, orbitolites, etc. with whole or sometimes fragmented tests filled with secondary calcite, up to 1 mm in size. Feldspars are represented by plagioclases in the form of small elongated patches showing clearly visible polysynthetic macles with an average size of 0.2 mm, noting the presence of the elongated perthitic orthoclase and the very common microcline, clearly distinguished with its squared macle. Quartz occurs in angular grains ranging in size from 0.05 to 0.5 mm. There are a few quartz clasts, which are generally polycrystalline, represented by crystals that are well interlocked with one another and up to 3 mm in size. Fine chlorite lamellae are observed, with a greenish colour and a size that varies from 0.05 to 0.2 mm. Muscovite occurs in the form of rods averaging 0.4 mm in size. The opaque minerals show small isolated grains of automorphic shape and 0.05 to 0.1 mm in size (Fig. 8d, photomicrographs of thin section 04 showing fossils, quartz, plagioclase, and chlorite under cross-polarized light and plane-polarized light at 10x magnification). The rock has a few notable voids and microcracks, reflecting its porosity.

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