Progressive metasomatism of serpentine in the sierra nevada of california

Nodules of serpentine enclosed in mica schist close to a body of intrusive quartz diorite have been altered by igneous emanations. Cores of residual serpentine are surrounded by successive envelopes of talc, talc and actinolite, actinolite, chlorite, and biotite. In some, veinlets of biotite transect the entire nodule. Chemical and micrographic analyses indicate that the changes involved the loss of magnesia from the nodules, the addition of silica in the inner zones, and the addition of small amounts of other oxides in the outer zones. The process of alteration resembled that often designated as granitization, but because of the extremely mafic composition of the original rock, the products have no similarity to a granitic rock.