  We study the extreme points of the cone of quasiconvex quadratic forms with
linear elastic orthotropic symmetry. We prove that if the determinant of the
acoustic matrix of the associated forth order tensor of the quadratic form is
an extremal polynomial, then the quadratic form is an extreme point of the cone
in the same symmetry class. The extremality of polynomials and quadratic forms
here is understood in classical convex analysis sense.
