Gemstone Occurrences in New Jersey

A ruby crystal from Tanzania similar to those found in New Jersey.

Like many of the states of the Northeast New Jersey contains some of the best localities for finding gems in the Eastern United States.  Agate is found throughout the traprock quarries of the state as well as quartz gemstones including amethyst that occurs as cavities in the stone.  Many marine fossils are also found in the state including many fossils of shark teeth. Most of these fossils are found in the Kirkwood formation (Eocene and Miocene) in Monmouth County.

One of the most interesting stones found in the state are so-called Cape May Diamonds that in reality are waterworn quartz crystals that are found on the beaches of Cape May Point along the Delaware River in southern New Jersey.  These stones are the most abundant at Higbee and Sunset beaches in Cape May.  These stones can range in size from the finest sand to one whopper that weighed 3 pounds 14 ounces that is known as the Cape May Diamond that was found in New Castle, Delaware in 1866.

Rubies are rarely found in the white marble at the mining district in Franklin where they are found associated with the zinc mines in Franklin and Sparta.  Many of these stones are small, but are well formed.  The rubies fluoresces red, but the marble matrix doesn’t. Many minerals found on the mine dumps around the area are various minerals of zinc that also fluoresce in brilliant colors under a fluorescent light with some of them even considered gemstones.  Another mineral that is found associated with the zinc minerals is rhodonite a silicate of manganese that is often cut as cabochons.

Bloodstone or heliotrope is found in sparing amounts in the Eastern United States north from Florida with exposures in New Jersey.  This is a member of the quartz family of gemstones that is dark green in color with bright red spots of hematite.  This stone is often cut and used in inexpensive jewelry.

A polished slab of petrified wood.
Photo by Daniel Schwen

In addition to agate the traprock quarries in Passaic County also contain many zeolite minerals as well as datolite and prehnite in large quantities. In many places the traprock quarries have cavities lined with amethyst crystals.  In some areas in eastern New Jersey you can find jasper and petrified wood.

In recent years one of the most valuable gems in North America has been overlooked by collectors is the freshwater pearl found in many of the mollusks in the states many rivers.  The pearl was looked avidly for in the 19^th Century, but for a period of inactivity caused by over fishing the mollusks  caused this industry to decline.