85. Inwood Marble

661 Isham St., New York, NY 10034

 Isham Street at the corner of Seaman Avenue. 

Inwood Marble

Inwood marble is a 450-million-year-old metamorphic rock found in Northern Manhattan, particularly in Inwood Hill Park and Isham Park. Formed by heat and pressure during the creation of Pangea, this white, dolomitic stone is soft and easily erodes. It is historically significant, having been quarried and used for building in the 19th century. 

Geological Origin: It was formed around 450 million years ago, during the Ordovician period, when the East Coast of North America collided with a chain of volcanic islands.

Composition: It is largely dolomitic (magnesium-rich) with some calcite marble, often containing silicate minerals like tremolite and quartz.

Location: While it is mostly found below ground (underlying areas like Harlem and the East River), it appears above ground in Inwood’s hilly areas and in local playgrounds.

History & Use: In the early 1800s, it was quarried at the northern tip of Manhattan. The Kingsbridge Historical Society notes that this marble was used for various local construction projects.

Appearance: The stone is known for its pure, crystalline white appearance, which makes it distinct from surrounding rock layers.

Erosion: Due to its soft nature, Inwood marble is easily eroded, especially by acid rain, notes a Washington Heights NYC article.