3. The pure peridotites of Mt. Apoi

Theme A:
Learning about and enjoying the earth's transformation from peridotites

Peridotite is composed chiefly of the minerals olivine, orthopyroxene and clinopyroxene, with the olive-green olivine dominating. This beautiful crystal is sometimes used as a gemstone called peridot, which is the birthstone for August. The term olivine is derived from its olive-green color. As the rock was originally located deep under the earth's surface, it is close-grained and hard with a specific gravity as high as 3.0 - 3.3 (g/cm3).

Most peridotite metamorphoses into serpentinite due to contact with water during its ascent from the mantle deep under the earth's surface. However, most peridotite on Mt. Apoi rose to the surface without metamorphosis. The existence of various peridotite types with different minerals in different combinations makes it scientifically valuable for the insight it provides into how magma is created and other matters relating to the earth's interior. Those found in this area are globally known as the Horoman peridotites.

Dunite
Olivine content of more than 90%
Harzburgite
Olivine content of more than 60% with a high proportion of orthopyroxene
Lherzolite
Olivine content of more than 60% with high proportions of orthopyroxene and clinopyroxene
Plagioclase lherzolite
A type of lherzolite with a high content of plagioclase