Internal Structure, Petrography and Mineralogy of Beryl in Bahr-e-Abad Area, East of Afghanistan

Abstract

This paper deals with the study of beryl, its variety, petrographic, and gemological specifications in the Bahr-e-Abad area of Jalalabad city. Beryl is a relatively rare silicate mineral, cyclo-silicate, with a chemical composition of Be3Al2 (Si6O18) and a hexagonal crystal shape. It is found in igneous and metamorphic rocks in many parts of the world. In order to achieve the aim of this paper, three methods, namely; library work, fieldwork, and lab work, were conducted, and about 20 specimens were collected from the above-mentioned area and taken to the Afghanistan Geological Survey (AGS) for making the thin sections and spectrometry analysis. Bahr-e-Abad area is related to the tectonic zone of Jalalabad. Jalalabad zone is located in the eastern part of Afghanistan and southeast of the Nuristan zone. Correspondingly, this zone is related to the upper Cambrian or younger Cambrian. In this area, the age of rocks is related to Archean- Middle Proterozoic AR-PR2. Beryl mineral is mostly found in Europe, Norway, Austria, Germany, Sweden, Ireland, Russia, Brazil, the US, Colombia, and Pakistan. Afghanistan is counted as one of the world’s leading countries in having rare-metal pegmatites, which are present in Afghanistan’s pegmatite belts in Afghanistan. This mineral is widely available in the pegmatite veins of Nuristan, Sistan, Panjshir, and Laghman. All pegmatite groups of Afghanistan are related to intrusive rocks. This study found that the rocks which are situated within pegmatite veins, besides beryl mineral, generally have the same composition and contain plagioclase, feldspar alkali (sodium-potassium), and mica (phlogopite and biotite) minerals. This is a microcline – albite type.