Staten Island Serpentinite facts for kids

The Staten Island Serpentinite is a special type of rock found on Staten Island in New York City. It's like a natural extension of the New England Uplands and is close to the Manhattan Prong. This area includes Todt Hill, which is the highest point along the Atlantic coast south of Maine. Todt Hill stands tall at 410 feet (about 125 meters) above sea level. The name "Todt" comes from a Dutch word meaning "dead." Early Dutch settlers might have called it this because the hilltops looking over The Narrows had many rocky spots with no trees. The type of rock found there was a big reason for this.

Much of Staten Island is covered by the Harbor Hill Moraine, which is a pile of rocks and dirt left behind by the last big glacier. But in the higher areas of Staten Island, you can see layers of bedrock made of a rock called serpentinite. Grymes Hill, the second highest point on Staten Island, is just a few miles from Todt Hill and has similar rocks.

What is Serpentinite?

Serpentinite is a rock that gets its name from the main mineral it contains, called serpentine. This rock often has a bluish to greenish-gray color.

Minerals in Serpentinite

Serpentinite is mostly made of a type of serpentine called antigorite. It also has other minerals mixed in, like:

• Chrysotile (a form of asbestos)
• Magnetite
• Talc

How Serpentinite Forms

Serpentinite forms when other rocks, called ultramafic rocks, change deep inside the Earth. These ultramafic rocks are rich in minerals like olivine and pyroxene. This change, called metamorphism, happens when the rocks are in a place with lots of water and high pressure. Scientists think these rocks originally formed deep under the Iapetus Ocean a very long time ago.

Staten Island's Ancient History

Finding serpentinite in the middle of Staten Island tells us something amazing about Earth's past. It shows that ancient ocean crust was pushed up onto the edge of the continent. This happened during a huge mountain-building event called the Taconic orogeny. This event shaped much of the eastern United States. The presence of serpentinite also fits with the idea that Staten Island is located east of something called Cameron's Line, which is an important geological boundary.

Why Todt Hill Had No Trees

The main mineral in serpentinite, serpentine, has a lot of magnesium. Most plants cannot grow well when there's too much magnesium in the soil. The thin soil covering the hilltops on Todt Hill was scraped clean by glaciers long ago. This soil was rich in magnesium from the serpentinite bedrock. This is probably why those areas of Todt Hill were originally bare and treeless.

 This article incorporates public domain material from websites or documents of the United States Geological Survey.