41. Peridotite and dunite, when fresh, can contain up to ~ 4, 000 ppm nickel within olivine.42. The greenish rock is a metamorphic rock consisting wholly of serpentine minerals commonly derived from the alteration of peridotite . 43. This residual is denser than the mantle peridotite and can cause delamination of the lower crust containing the residual. 44. Classic peridotite is bright green with some specks of black, although most hand samples tend to be darker green. 45. The eclogite melt may then react with enclosing peridotite to produce pyroxenite, which in turn melts to produce basalt. 46. These layers most commonly have been interpreted as products of reaction between ascending magmas and peridotite of the upper mantle. 47. Plagioclase can occur in lherzolites and other peridotites that crystallize at relatively shallow depths ( 20 30 km ). 48. Instead, extension simply pulls the crust away, exposing or " unroofing " the mantle, exposing serpentinized peridotite . 49. Experimental studies of appropriate peridotite samples document that the solidus temperatures increase by 3 �C to 4 �C per kilometer. 50. The syenites, for example, and the peridotites , are far less important than the granites, diorites and gabbros.
