Near Wilmington in New Castle County, Delaware — The American Northeast (Mid-Atlantic)
Gabbro
igneous
Molten magma deep within the Earth often rises towards the surface when continents collide. Gabbro forms when the magma slowly cools deep within the Earth, allowing relatively large crystals to develop. when gabbro weathers under hot and humid conditions it can form iron minerals.
Gabbro is commonly called "black granite" and can be cut and polished for many uses, such as kitchen counter tops, floor tiles, and gravestones. Gabbro from Iron Hill, south of Newark, was evaulated for use as road fill for construction of I-95, but it was too hard to crush.
[Captions:]
Lighter crystals are plagioclase feldspar
Darker crystals are pyroxene
Can you find the dark and lighter gray crystals?
Erected by Delaware Museum of Nature & Science.
Topics. This historical marker is listed in these topic lists: Natural Features • Roads & Vehicles.
Location. 39° 47.956′ N, 75° 36.591′ W. Marker is near Wilmington, Delaware, in New Castle County. It can be reached from Kennett Pike (Delaware Route 52) north of Old Gatehouse Road, on the right when traveling south. Touch for map.
this page online
Regionally, this marker is in Greater Philadelphia. It is also in the American Mid-Atlantic and on the Delmarva Peninsula. Globally, it is in the North Atlantic Region, North America, the Western Hemisphere, the Western World, and the Anglosphere. Historically, it finds itself in what was once New Netherland and also one of the original Thirteen Colonies.
Other nearby markers. At least 8 other markers are within walking distance of this marker: Sillimanite (here, next to this marker); Brandywine Blue Gneiss and Barley Mill Gneiss (here, next to this marker); Iron Hill Iron Ore and Chert (here, next to this marker); Pegmatite (here, next to this marker); Cockeysville Marble (a few steps from this marker); Weymouth Pine (within shouting distance of this marker); The Cottage (approx. 0.6 miles away); 300-Year-Old Oak Tree (approx. 0.6 miles away). Touch for a list and map of all markers in Wilmington.
Credits. This page was last revised on April 30, 2025. It was originally submitted on April 30, 2025, by Devry Becker Jones of Washington, District of Columbia. This page has been viewed 109 times since then and 8 times this year. Photos: 1, 2. submitted on April 30, 2025, by Devry Becker Jones of Washington, District of Columbia.
