Zussmanite - Discovery and Occurrence

Discovery and Occurrence

It was first described in 1960 by Stuart Olof Agrell in the Laytonville quarry, Mendocino County, California. Zussmanite is named in honor of Jack Zussman (born 1924), Head of the University of Manchester’s Department of Geology and co-author of Rock-Forming Minerals. In the Laytonville quarry, Zussmanite occurs in metamorphosed shales, siliceous ironstones and impure limestones of the Franciscan Formation. It is a location of high pressure and low temperatures where blueschist facies metamorphic rocks occur. This is also the locality in which Deerite and Howieite were first discovered. This type of locality also produces micas, which have a similar structure as zussmanite.

The locality in which zussmanite occurs is one of ultra high to high pressure and low temperatures. This Barrovian type of metamorphism is usually distinguished by the P/T range rather than the ranges in pressure and temperatures (Miyashiro et al.,1973). The three principal Barrovian types are low P/T type, medium P/T type, and high P/T type. The high P/T type, referred to as glaucophanic metamorphism, is characterized by the presence of glaucophane and forms glaucophane schists (Miyashiro et al.,1973). Glaucophane schists, commonly referred to as blueschist-facies, result from metamorphism of basaltic rocks and are usually located in folded geosynclinal terranes (Deer, Howie, Zussman et al.,1992). Glaucophane schists are characterized by low temperature (100–250 °C) high pressure (4-9 kbar) metamorphism (Deer, Howie, Zussman et al.,1992). Zussmanite is commonly found with stilpnomelane and quartz, usually forming abundant porphyroblasts up to 1 mm in size, in the newly discovered locality in Southern Central Chile ( Massonne et al., 1998).