A Study of Solid State Phase Transformation of Biogenic Aragonite into Calcite Crystals R.Manikandan 1 , P.Martin 2 , and S.Devashankar 3* 1 Research scholar, Department of Advanced Zoology, Govt. Arts College, Nandanam, Chennai, India Email: mailmrithunjayan@gmail.com 2 P.G and Research Department of Advanced Biology and Biotechnology, Govt. Arts college, Nandanam, Chennai, India- Email: dr.martinjayakumar@gmail.com 3* Department of Physics, Velammal Engineering College, Chennai, India-600 066. Email: devashankar.srinivasan@gmail.com Abstract— Biogenic calcium carbonate obtained from Pearl oyster subjected to FTIR, FT- Raman and Powder X-ray diffraction studies. It is in the polymorphic form of aragonite. The analysis of calcined aragonite reveals that it undergoes solid state phase transformation in to calcite a thermodynamically more stable polymorphic form of calcium carbonate. Index Terms— Calcite, Aragonite, Biogenic, Phase transformation I. INTRODUCTION Calcium carbonate (CaCO 3 ) is a ubiquitous inorganic component of the near-surface environment, occurring aqueous systems, sediments and aerosols. It precipitates in both fresh and saline water and can form by biogenic or abiotic means [1]. CaCO 3 has three anhydrous forms namely calcite, aragonite and vaterite and three hydrated forms, amorphous CaCO 3 , monohydro calcite (CaCO 3 .H 2 O) and ikatite (CaCO 3 .H 2 O) [2]. The phase diagram of CaCO 3 shows that calcite is thermodynamically most stable and most abundant phase under ambient conditions, aragonite is the high-pressure polymorph and vaterite is thermodynamically unstable [3]. Many sea shells and corals are composed either totally or in part of aragonite [4]. Calcite has the ability to fix or structurally incorporate biologically active elements such as phosphorous, calcium, magnesium, zinc, iron [5]. Due to its metastability under earth’s surface condition, aragonite tends to transform into calcite by reaction with aqueous solutions[2]. Sequential polymorphic transformation of CaCO 3 in the presence of DTPA was reported [6]. Structural transformation from aragonite to vaterite and calcite by the assistance of SDBS in the temperature range 90 to 150 o C was reported [7]. In traditional Indian medicine CaCO 3 obtained from various biogenic sources such as Pearl oyster, Conch shell, Snail shell and Cowry shell are mixed with other organic/inorganic compounds and calcined. The resultant powder is being used for the treatment of many diseases like piles, fistula, tuberculosis, bronchial asthma, gastric ulcers, skin diseases, renal calculus. There are very few reports on the study of initial and final products. The aim of the paper is to find in what polymorphic form CaCO 3 exists as obtained from biogenic sources and in the calcined final products which are used as medicine. In this regard calcium carbonate obtained from four biogenic sources such as Pearl oyster, Conch shell, Snail shell and Cowry shell are studied using Fourier Transform Infrared (FTIR), FT Raman spectroscopy and Powder X-ray diffraction techniques. The results of one of the species are presented. DOI: 03.AETS.2013.3.288 © Association of Computer Electronics and Electrical Engineers, 2013 Proc. of Int. Conf. on Emerging Trends in Engineering and Technology