Near Wilmington in New Castle County, Delaware — The American Northeast (Mid-Atlantic)
Sillimanite
metamorphic mineral
| | Delaware's State Mineral | |
Sillimanite formed under conditions of high temperature and variable pressure during the Taconic Orogeny. Sillimanite's needle-like crystals are light gray, white and tan colored and have a texture similar to wood. Another name for sillimanite is fibrolite. It is found in many places in Delaware's piedmont, but boulders like this one with clusters of remarkably large sillimanite crystals are uniquely found around Hoopes Reservoir and Brandywine Springs County Park.
Named in honor of Benjamin Silliman, Sr., (1779-1864), one of the most influential American scientists of the early 19th century.
Walk over to the front of the Museum and look at the sillimanite boulder in the Bobbee Vernon Memorial Garden. It's one of the best sillimanite specimens in the world!
This boulder contains sillimanite crystals. Do you see them?
Hint: They are Fiber-like crystals.
Erected by Delaware Museum of Nature & Science.
Topics. This historical marker is listed in these topic lists: Natural Features • Science & Medicine.
Location. 39° 47.955′ N, 75° 36.594′ W. Marker
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: Gabbro (here, next to this marker); Pegmatite (here, next to this marker); Brandywine Blue Gneiss and Barley Mill Gneiss (a few steps from this marker); Iron Hill Iron Ore and Chert (a few steps from this marker); Cockeysville Marble (a few steps from this marker); Weymouth Pine (within shouting distance of this marker);
Also see . . . Wikipedia articles about Benjamin Silliman [Sr.].
Benjamin Silliman (August 8, 1779 November 24, 1864) was an American chemist and science educator. He was one of the first American professors of science, the first science professor at Yale, and the first person to use the process of fractional distillation in America. He was a founder of the American Journal of Science, the oldest continuously published scientific journal in the United States.(Submitted on April 30, 2025, by Devry Becker Jones of Washington, District of Columbia.)
Additional commentary.
1. About the marker
This sign serves as a historical marker because it includes historical significance, most notably who the rock is named for.
— Submitted April 30, 2025, by Devry Becker Jones of Washington, District of Columbia.
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 131 times since then and 22 times this year. Photos: 1, 2. submitted on April 30, 2025, by Devry Becker Jones of Washington, District of Columbia.
