Prehnite finger cast after Anhydrite

Great luster, good color, and pleasing gemminess make this miniature sized specimen and worthwhile piece for the price. The main finger is undamaged, but the side of the specimen is contacted where it was removed from the pocket. You can see one of the “fingers” on the side of the piece shows the thin prismatic form that once was an Anhydrite crystal, which dissolved away after the Prehnite was introduced to the pocket.

The Prospect Park Quarry is arguably the most famous mineral producing basalt quarry in New Jersey and, for over a century, has provided collectors with impressive display specimens, including some of the most recognizable Prehnites extant. Many of these Prehnites formed casts (epimorphs), which is a type of pseudomorphism whereby preexisting crystals of Anhydrite were coated and later dissolved by the more stable Prehnite, creating slender, striated and somewhat blocky hollow cavities. Depending upon the original shape of the Anhydrite, the Prehnites can sometimes leave unique finger-shaped casts. These “fingers” are quite possibly the most desirable form of casts for Prehnite from New Jersey.

During the latter half of 2010, one of the most momentous Prehnite discoveries was made at the Prospect Park Quarry. Some of the finest quality Prehnite casts were collected in a series of pockets in the middle of the quarry in a dome-shaped structure measuring approximately 40 x 40 x 40 feet (approximately 12 x 12 x 12 meters) that is locally referred to as a diapir. This discovery stands as one of the most impressive and important discoveries, not only in recent years, but perhaps in the history of the Prospect Park Quarry. Perhaps the most important aspect of the specimens is the fact that the Prehnites show DISTINCT crystallization that can easily be seen with the naked eye – a rare feature for this type of Prehnite as the crystals are often very small and nearly amorphous. Many of the most desirable qualities of great Prehnites from any New Jersey locality are seen in these wonderful specimens.

This discovery can best be described as bittersweet as it will more than likely be the last major production of specimens from Prospect Park. The quarry has been filled in for a housing development and will never again produce specimens. The Prehnites collected in 2010 will almost certainly go down as the “last hurrah” for the great Prospect Park Quarry.

Specimen #PREH3118