Blueschists on Ring Mountain

Simplistically, what is called blueschist metamorphism describes a form of mineral changes that occur under conditions of extremely high pressures and relatively low temperatures (i.e., deep burial inside the Earth...without being heated to the temperatures expected at such depths). This photo (with text) shows two of the blueschist blocks near the crest of the Ring Mountain area.

These types of metamorphic rocks derive their "colorful" name from the presence of the mineral glaucophane.

The first indications of the uniqueness of the Tiburon Peninsula was the identification of a new mineral from the blueschist rocks called Lawsonite by F.L. Ransome who described it in a 1895, University of California Geology Department Publication.

These blueschists are found in numerous places within the Franciscan rocks of California and some of the 'highest pressurized' ones reported are found in the melange of Baker Beach in San Francisco.

In 1962, Edgar Bailey of the U.S. Geological Survey introduced the concept of "blueschist" into the world of metamorphic geology. His carefully constructed definition established the pressure and temperature conditions which produce this type of metamorphism. It is important to note that not all blueshist rocks are blue!

Information on the interesting minerals found in Marin can be found here.


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