Chlorine-Rich Amphiboles from the Grenville-Age Hudson Highlands of New York State

Some Grenville-age rocks exposed in the uplifted region of the Hudson Highlands of southern New York are amphibole-dominant igneous rocks. The amphibole-rich rocks, which are locally pegmatitic in nature, are associated with magnetite ore and coarse-grained syenite; the ore was discovered and mined from the middle of the 18th century to the end of the 19th century. The amphiboles have attracted the attention of many researchers for nearly two centuries. Chemical analyses demonstrate that they are pargasite or hastingsite in composition and are particularly rich in Cl and K. High-precision crystal structure analyses of 11 Cl-rich amphiboles from the Hudson Highlands (0.0134