Notice how each olivine goes uniformly into extinction, in contrast to those in the lherzolite from Lherz. Annealing of this rock is probably the result of regional metamorphism that converted enstatite to talc, the fibrous or micaceous mineral that forms large patchy grains that appear to enclose many olivines. Notice that each olivine grain is rimmed by serpentine. Serpentine has low relief, occurs as fibrous grains, in veinlets or as a felty matrix, so it appears to have sweeping extinction. It may be colorless to very pale green in plane light and 1 gray under crossed polars.
Grains are never large enough to see interference figure.
Olivine is converted to serpentine by reaction with water at 250-400 C. Hot water penetrated this rock both along fractures and along grain boundaries. Garnet grains are rounded, stand out in high relief against olivine, and are isotropic. Chromian diopside is distinguished from olivine in plane light by its larger size, pale green color, and presence of one or two cleavages. Garnet peridotites are associated with eclogites in the Caledonian metamorphic terrane of western Norway. Their origin is problematical.