A NEW SERENDIBITE LOCALITY IN THE GRENVILLE PROVINCE (ORANGE COUNTY, NEW YORK)

A new locality of the rare borosilicate Serendibite (Ca₂(Mg, Al)₆(Si,Al,B)₆O₂₀) was discovered during regional sampling for calcite-graphite carbon isotope thermometry of the Franklin Marble. The Mesoproterozoic Franklin Marble consists of a main band that extends ca. 30 km from Orange County, NY into Sussex County, NJ and also has outliers in Warren County, NJ. The serendibite studied is from an unremarkable course-grained calcite marble outcrop 1.8 km from Edenville. Serendibite occurs in layers rich in pargasitic amphibole. This locality is >1/2 km from the nearest mapped intrusive body. Equant serendibite showing polysynthetic twinning occurs with green amphibole, apatite, phlogopite, calcite, scapolite, and sinhalite (MgAlBO₄). Some serendibite is altered to uvitic tourmaline. This occurrence of serendibite in a calc-silicate layer of the Franklin Marble of New York joins other three other Grenville Province localities: near Johnsburg in the Adirondack Highlands, near Russell in the Adirondack Lowlands, and another possible locality in Orange county (Amity). Serendibite, sinhalite, and tourmaline at this locality most likely result from metamorphism of a boron-rich sedimentary protolith.