Mineral paragenesis in a talc–water experimental hydrothermal system

Abstract

Gel having a Mg:Si ratio identical to that of talc (3:4) was treated hydrothermally at six temperatures between 300' c and 550' C and I kbar for times of7, 30, 50, 120 and 200 days in order to identify reaction trends. Talc crystallized first at all temperatures. It then reacted to form stevensite at temperatures between 300'C and 450'c. At 400'C and 450'C, stevensite continued to react to form a perfectly ordered mixed-layer stevensite/ chlorite (corrensiteJike structure). At 500 C and 550' C the initially formed talc improved in crystallinity with time and showed no further reactions. Natural talc starting material showed trends similar to that of the gels, reacting to form stevensite at 350' C in a 30-day run. The reaction trends suggest that stevensite and/or the corrensite-like phase are the stable minerals at 450'C and below in systems with chemistry similar to that of these experiments.