J.IIC-CG VOLUME 10 & 11 (1985/1986)
Slatechuck Creek Argillite: Its Structure, Composition and Dimensional Stability
An argillite found near Slatechuk Creek on Graham Island, the largest of the Queen Charlotte Islands, has been used by Haida carvers since at least the 1820s. The history of the quarry and the techniques of carving are reviewed. Petrography, whole rock analysis, X-ray diffraction results and instrumental neutron activation analysis are reported. The rock is a carbonaceous, kaolinite slate containing the clay minerals pyrophyllite, kaolinite and lesser amounts of montmorillonite and illite. Dimensional response to fluctuations in relative humidity is quite rapid and is five times greater in the direction perpendicular to the bedding plane of the rock than in the plane parallel to it. The presence of expanding clays as well as hidden structural flaws have resulted in carvings which are prone to chipping and cracking. Excessive incandescent light levels which can cause local desiccation must be avoided. Relative humidities in the range 30-50% are recommended for argillite and a review of existing display, handling and transportation procedures is advised.
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