The serpentinite body in Yamabe district in central Hokkaido intruded into Jurassic formation. This plutonic body crops out about 2.5km length by 600m maximum width, in which good chrysotile asbestos has been well mined since 1940.
The serpentinite body is traversed by numerous hypabyssal rocks having leucocractic and sometimes melanocratic natures. The representative type of which is trondhjemite.
The hard specimens of serpentinite were collected from fresh outcrops in this body, and they are exmained by optical microscope, X-ray and electron diffraction methods. The most of the rocks are composed of mixture of minor flakes of antigorite, chrysotile, and lizardite. It should be noticed that these serpentinite specimens frequently contain a pretty amount of brucite, and sometimes the brucite occupies about a half amount of the rock. Minute crystals of olivine, pyroxene and opaque minerals are contained in very small quantity. The mineralogical composition varies gradually at every placs within the serpentinite body.
Brucite can be extracted by acetic acid from serpentinite. One of the serpentinite samples contains about 54 percent of brucite by the method. This specimen shows only 18.15 percent of SiO₂ content by chemical analysis, whcih is extremely basic nature. This rock can be call as a brucite serpentinite.
Serpentinite has been generally considered to be formed by addition of water to peridotite. However, this brucite serpentinite cannot be explained as a direct product by serpentinization from original peridotite without any large migration of chemical components. Partial concentration of MgO within serpentinite body may result the localization of large amount of brucite mineral in the body.
Serpentinization to form the serpentinite body in Yamabe district was performed at the depth beneath the present surface. Then the solidifies serpentinite intruded during an orogenic period.

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