Duke University

be variously volcanic and sedimentary: it was likely originally formed by sedimentation of volcanic material. A USGS geologist concludes: "The Duke quarry phyllite was derived from argillite, tuff or tuffaceous sandstone, and volcanic breccia. Occurrence of laminated argillites suggests marine deposition. … There is insufficient evidence to determine if the volcanic material was deposited directly by igneous action or if it was re-worked by sedimentary processes. Presence of lava flows and very coarse breccias in Orange County suggest that the volcanic centers were relatively near." A UNC geologist concurred that "original features of the phyllite have been obscured by deformation and recrystallization, but the rock apparently was derived from argillites and tuffs," and that "sedimentary reworking of volcanic materials is to be expected."
After its initial formation, Duke stone underwent several metamorphic events, including the collision of Carolinia with Laurentia. The Carolinia-Laurentia collision started …