Hydrothermal alteration experiments of amorphous silicates

comparison of experimental products with minerals of carbonaceous chondrites

Abstract

CI, CM, CR and TL chondrites experienced strong aqueous alterations on their parent bodies. Therefore, a study of the alteration process is important for understanding the evolution of early solar system materials. To investigate the aqueous alteration process, many hydrothermal alteration experiments have been performed so far using crystalline silicates or chondrites themselves as starting materials. In contrast, silicates in interstellar medium and molecular cloud are considered to be amorphous based on IR astronomical observations. Therefore, to understand the aqueous alteration process of amorphous silicates, we have carried out hydrothermal alteration experiments of amorphous silicates with the Fe- and S-free CI composition. The amorphous silicates were heated at 650-750^oC to prepare additional starting materials with different degree of olivine contents. A mixture of the starting material and deionized water (or acid/alkali solutions) was heated at 100-200^oC for 24-336 hrs. Run products were analyzed using XRD, SEM-EDX and micro-IR spectroscopy. Saponite, serpentine, talc and calcite were easily formed from the starting materials including amorphous silicates.