The morphology and number of forsterite crystals in the Ubchebe Peak,
California, contact aureole vary systematically as a function of
metamorphic grade. From their first appearance to as close as similar to
150 m from the intrusive contact, forsterite crystals are large (5-20
mm) and have a tabular habit (a approximate to c >> b). In contrast,
forsterite near the contact is equigranular and much smaller (<1 mm in
diameter). The number of crystals per mole of forsterite increases from
3.5 x 10(4) at the forsterite-in isograd to more than 1.5 x 10(8) near
the contact, This trend is interpreted to result from an increase in the
ratio of nucleation rates with respect to growth rates with proximity to
the intrusion, The change in morphology from tabular to equigranular is
explained by kinetic surface roughening. The nucleation and growth
information gained from this study highlights the important role of
nucleation kinetics in the crystallization of forsterite at the Ubehebe
Peak aureole.