ABSTRACT

Experimental deformation of alabaster furnishes useful observations concerning fracture development in a mineral aggregate. Study of deformed samples demonstrates that one or more types of fracturing can combine with kink-band development and other features to define the deformation mode that typifies a given range of confining pressure. Cluster analysis is used to delineate objectively the grouping of deformation features which constitutes the deformation mode.

A comparison of experimentally determined values of differential stress at the linear elastic limit with computed values of the stress necessary to extend "Griffith" cracks suggests that microfracturing terminates purely elastic deformation at both low and high confining pressure. Detailed study of grain-boundary fractures indicates that in alabaster this particular type of deformation feature attains maximum development at relatively low levels of confining pressure and strain.