New Jersey Gemstones

A variety of tumbled gemstones
Scanned by Adrian Pingstone

Amber that has been preserved since the age of dinosaurs is found in several places in New Jersey where there are Cretaceous rocks one of these places in the area around Sayreville although they can be found scattered throughout the Cretaceous rocks and various localities throughout southern New Jersey. Although there are several deposits of Cretaceous aged rocks in the United States Amber is only found with appreciable quantities in New Jersey.

Amethyst is found in the many trap ridges of New Jersey in both the area of the Palisades and in the Ramapo Mountains.  This variety of quartz is usually found in the cavities in the rock. Many other minerals of the zoisite family are also associated with traprock quarries.

In the past there was extensive zinc mining activity in Franklin and Sterling Hill in Ogdensburg that produced large quantities of zinc minerals.  The mine dumps in these areas are one of the most noted areas in the United States that have produced fluorescent minerals.  Some of these minerals are gemstones in their own right notably rhodonite and sphalerite.  In addition Sussex County is also known for producing other minerals including aragonite, corundum, garnet, pyrrhotite, rhodonite, spinel, tourmaline and williamsite.

Bergen County has produced amethyst, natrolite and opal that are found in the county’s trap ridges.

Mercer County has been known to produce albite, calcite, chabazite, datolite, natrolite, stilbite and tourmaline. Calcite, chabazite and datolite are produced from the trap ridges in the county.

In the far southern part of New Jersey can be found quartz crystals that are called by many Cape May diamonds although the source of these stones remains unknown it is thought they are washed down from some underwater formation further upstream in the Delaware River.  They are found on the beaches of Cape May and surrounding communities at the mouth of the river. The same area also produces jasper. 

Corundum has been found in Sussex County associated with the Franklin limestone as almost perfect crystals seen in cavities in the limestone.  These stones are blue, grey and red that in some places are clear enough to be cut into gems. 

Other counties where gemstones can be found include:

Middlesex - marcasite, petrified wood, pyrite

Morris - carnelian, serpentine

Passaic - agate, amethyst, carnelian, chabazite, datolite, heulandite, pectolite, prehnite

Sussex - aragonite, corundum, garnet, pyrrhotite, rhodonite, spinel, tourmaline, williamsite

Union - calcite, chalcedony, prehnite, sphalerlite

Warren - calcite, chalcedony, garnet, molybdenite, prehnite, serpentine, sphalerlite

Most of the collecting sites are located in Northern New Jersey.  Many of these sites are found at old mines or rockcuts.

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.