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New Jersey Rock and Minerals
New Jersey's has a rich mining history.
The northwest corner of New Jersey contains the famous Delaware Water Gap, where the Delaware River has cut through the Kittatinny mountain range of the Appalachians. Southeast of these mountains is a belt of ridgeland known as the Highlands. Igneous and metamorphic rock from the Late Precambrian and Early Paleozoic era, make up the Highlands. There are over 500 abandoned mines in this area, because of its rich mineral wealth. Magnetite iron and marble were important minerals mined from the New Jersey Highlands. The last iron mine, the Mount Hope Mine, closed for good in 1977.
Franklinite, belonging to the spinel family, is a mineral first discovered at the Sterling Hill Mine, a former zinc mine in Ogdensburg, Sussex County. It was the last working underground mine in New Jersey and it closed in 1986. Now it is a museum where you can tour the mine, which is cool because many of the minerals found here fluoresce. Franklinite it occurs with willemite, calcite, and zincite. In 2023, Franklinite was designated the state mineral of New Jersey.
A mineralogically unique zinc ore that fluoresces bright red and green, was found in the Franklin Marble in Sussex County and was worked until 1987.
Below and paralleling the Highlands is the Piedmont lowlands marked by traprock ridges, such as the Watchung Mountains and the Palisades, the cliffs that rise steeply above the western bank of the Hudson River. In the Palisades there is a 30-foot-thick olivine-rich zone roughly 30 feet from the lower contact. Prehnite is found in the Watchung Mountains.
Southeast New Jersey is a coastal plain, much of it is marsh. Coastal Plain sediments have been mined for bog iron, sand for making glass, foundry sand, ceramic and brick clay and titanium from the mineral ilmenite in sand deposits. Also, shark teeth and other marine fossils have been found in the coastal region.
New Jersey’s fossil finds range from dinosaur bones to marine fossils like brachiopods, corals, and trilobites. Both Poricy Park and the Big Brook Preserve, located in Monmouth County, are great for fossil hunting. The gravel beds along Ramanessin Brook, located in Holmdel, are also good fossil hunting grounds. In the northwest part of the state, the Lockatong Formation has yielded dinosaur tracks and footprints.
The best rock collecting spots in New Jersey include its many quarries, old mining dumps, the gravel beds of streams and rivers, and granite outcroppings.
Before venturing out-do some research on where and what you can collect. Remember you must have permission to collect on private property.
See my page on Rockhounding Rules for general information on the rules of collecting rocks on various lands.