Introduction

The Cheshire Traprock quarry has been of interest to collectors for a while. It produced complex clusters of natrolite, often associated with analcime, heulandite,or prehnite. All of these minerals are often well formed. Specimens of calcite, datolite, and chalcopyrite are also of note. These minerals form in the classic seems that are associated with heavily mineralized diabase.

Mineralized Portions of The Diabase

Occasional seams containing datolite and heulandite are found where indicated on the map, but most of the interesting material occurs in the North West portion of the quarry. Here, there are many veins, and seems of altered diabase, most containing well formed mineralization, all being slightly different in content and form. More then one have analcime as the mane component, although the rest of the content varies from one seem to another.

Datolite/Heulandite Seams

The heulandite occurring away from the North West part of the quarry is markedly larger in crystal size. Most seams have chalcopyrite. The crystals are mostly colorless. They are well formed, but rarely exceed 3 mm in length. They are a druss that completely covers the diabase, in seems 2-5 mm in diameter. Rarer are seams of datolite, but those that were uncovered contained colorless, white, to greenish drusses of crystals in 1-3 cm seems.

Altered/Brecciated Seams

These seams are frequent in the North West portion of the quarry, and are classic examples of typical prehnite-in-diabase occurrence. The consist of chlorite sand and altered diabase surrounding a vein structured prehnite seem. Where the seam widens, pockets are present. The veins average 6-40 mm in diameter. The prehnite exists mostly in the common spherical forms, and the occasional singular spheres exist in the chlorite. The color of specimens is almost exclusively dark green.The occasional natrolite or calcite is present in most veins. Calcite sometimes takes the place of, or occurs with, the prehnite.

Some breccias form pipe like structures with 'dry' (clorite free) spaces. Such breccias contain heulandite, and possible prehnite hemisperes. These can measure up to 40 cm in diameter.

Natrolite/Analcime Seams

The most frequent mineralization is by far the limonite filled seams of natrolite with analcime. Most natrolites are under 15 mm in length and 1 mm diameter. The analcime covers almost entirely the surface of the diabase, and the natrolite infrequently does the same. For the most part, the two minerals share the same seam, but a small amount may contain strictly one or the other. The natrolite is mostly translucent to transparent, but mostly stained red from limonite. The analcime is the also translucent and sometimes iron stained. No other minerals appear to occur in this type of seam.

Conclusion

The Cheshire Traprock Quarry is a unique locality, with much of interest. Few other locations in Connecticut have natrolite, analcime, and heulandite, and certainly not in the abundance to be seen in this location. The writer finds it unlikely that any more minerals could be added to the localities list, but would love to see something new. More exploration would certainly turn up something interesting.
Unfortunately, this promising locality is on private property. If anyone wants to collect there, seek permission from the owner and be courteous: don't destroy the place and leave garbage behind.