New York State Academy of Mineralogy New York State (NYSAM)

Minerals of the Hudson Highlands

The Hudson Highlands are an uplifted area of southeastern New York crossing Orange, Rockland, Putnam and Westchester Counties and are part of a larger geological province, called the Reading Prong, which extends from Connecticut to Pennsylvania. They are composed of Precambrian sedimentary and igneous rocks that were metamorphosed at a high temperature (800C) and a moderate pressure (4-7 kilobars) about one billion years ago during Grenville orogeny. Many small, but mineral-rich, iron deposits are scattered throughout the region and were mined from the early 18th century into the mid 20th century. World famous mineral localities in the Hudson Highlands include the Tilly Foster Mine in Brewster with its brilliant chondrodite, dark emerald green clinochlore, lustrous black magnetite, and various mineral replacements (pseudomorphs), as well as, the Monroe area with its giant spinel, scapolite, and amphibole group minerals. These beautiful mineral specimens were formed by the combined action of metamorphism and hot fluids upon the country rocks.


The Academy of Mineralogy is a not for profit organization dedicated to promoting a greater understanding and appreciation of the minerals and mineralogy of New York State. The chief goals of the organization are to work with the New York State Museum to promote the study of New York State's mineralogy and to facilitate the gathering of exceptional individual specimens and outstanding collections for preservation in the New York State Museum.