A chemical study of serpentinization — Burro Mountain, California

Serpentinized dunites and harzburgites from the Burro Mountain peridotite show no change in the ratio of iron and magnesia to silica when compared with the same ratio for the unserpentinized equivalents. The mineral assemblage resulting from serpentinization consists of lizardite-chrysotile, brucite, and magnetite and is determined by the original bulk composition of the peridotite. The chemical and mineralogical data indicate that serpentinization proceeded under isochemical conditions except for the introduction of water into the peridotite. Expansion accompanies serpentinization because the serpentine products occupy a greater volume than the peridotite protolith. Tectonic emplacement of the Burro Mountain peridotite was facilitated by serpentinization and the attendant expansion.