Fibrous Tourmaline: A Sensitive Probe of Fluid Compositions and Petrologic Environments

• DOI: 10.3749/canmin.1600019
• Publication Date: 2017-01-04T02:35:29Z
• Authors: Barbara L. Dutrow; Darrell J. Henry
• Keywords: Tourmaline

Abstract Tourmaline supergroup minerals with fibrous morphology record and respond to changing conditions in fluid-rich hydrothermal environments. Based on published data, hand-specimen optical observations, new chemical analyses of tourmalines from localities worldwide, several commonalities are apparent. Fibers typically nucleate a preexisting substrate tourmaline, but the fibers generally have dramatically different composition than tourmaline. When single tourmaline crystal, growth is restricted +c pole also or other without Most form late paragenetic sequence geologic environment where there an open fluid-filled space, e.g ., at end crystallization pegmatite pocket hydrous fracture system. Fibrous compositions can be foititic, schorlitic, dravitic, elbaitic, reflecting dissolved components fluxing aqueous fluids. While some homogeneous, many chemically zoned irregular, patchy, oscillatory zoning, zoning tracks evolution trends host environment. Using newly derived expressions relating X-site cationic occupancy fluid compositions, Na Ca contents fluids local equilibrium suggest that all petrologic settings equilibrated having variable concentrations (0.07–0.48 mol/l lower ranges associated foititic tourmaline) low (