APPLICATION OF A FLUORESCENT TECHNIQUE TO THE STUDY OF THE WEATHERINGPROCESS

Processes and rates of weathering in representative tuff obtained from a Green Tuff region were directly examined using a new fluorescent ap proach. This approach was developed to visualize microscopically the m icrocracks and micropores that contribute to deterioration. The follow ing observations were made. Progression of tuff weathering is caused b y a delicate balance between chemical alteration and physical disinteg ration. Weathering occurs in many hidden microcracks and micropores no t detected under natural light, but which can be clearly visualized un der ultraviolet light. Water pathways, such as microcracks and cavitie s, accelerated the chemical alteration by increasing the effective sur face area of rocks in contact with water. As the reaction proceeds, th e constituent materials loosen and alteration products become widespre ad in the matrix. Secondary amorphous to poorly crystallized materials , such as iron hydroxide and aluminosilicate, precipitate on the fract ure surfaces, slowing the progress of weathering. At the ultimate stag e of weathering in tuff, all cracks and most of the micropores are fil led with secondary materials. These observations on a microscopic scal e during tuff weathering agree with the assessment of weathering obtai ned by measuring porosity, P-wave velocity and tensile strength.