A nonlinear continuum phase field theory is developed to describe amorphization of crystalline elastic solids under shear and/or pressure loading. An order parameter describes the local degree of crystallinity. Elastic coefficients can depend on the order parameter. inelastic volume change may accompany the transition from crystal to amorphous phase. https://www.roneverhart.com/Corvette-Leather-Seat-Covers-Graphite-Standard-1984-1987/