Introduction

Zinc secondary minerals are not common in Canada - they are generally found in drier climates. This occurrence, limited to some very minor roadcuts, small outcrops, and trenching has produced some interesting minerals. These are of interest to collectors of microminerals and fluorescents. It is located north of the community of Five Islands in Colchester County.

History

Soil sampling and surveys were conducted in the early 1960s and again in the early 1970s. Some minor trenching and drilling was performed in the 1970s.

Geology

A discussion of the stability and solubility of the zinc minerals smithsonite, hydrozincite, and hemimorphite can be found in Takahashi (1960). That paper is interested in limestone hosted deposits, but the veins at this locality are rich in calcite and regardless, much of the discussion is more broadly applicable.

Takahashi also has discussions about the various minerals. One conclusion that I find interesting is given below:

Hydrozincite is the stable mineral in solutions which are in equilibrium with air and which have a pH higher than 8.1 Scarcity of such an alkaline water in nature explains the rarity of hydrozincite in humid regions.

Mineralogy

The mineralization is found in very thin factures in shale and in rare pockets. The rock is Silurian-Devonian in age and is only about 600 meters from the Cobequid Fault. The minerals found here include hydrozincite, calcite, sphalerite, smithsonite, hemimorphite, and galena. Nova Scotia Natural Resources also reports pyrite, argentite, and possible cerussite. Argentite is not stable at temperatures below 177 C, where it changes to acanthite, which has been used in the table below. Greenockite was identified in 2021 from older material.

Table 1: Minerals reported from New Brittain Road

Calcite - CaCO₃

Calcite is very common. It forms simple scalenohedrons, sometimes covered with a layer of smithsonite. It fluoresces red, so specimens of both calcite and hydrozincite (which fluoresces blue-white) produce an attractive color combination.

Galena - PbS

This seems to be a very minor mineral at this locality. I have seen a few octahedral crystals with sphalerite.

Greenockite - CdS

A single specimen showing a small patch of a powdery but bright yellow mineral was found by Terry Collett. After many years it was finally analyzed in 2021, using EDS at Saint Mary's University and was found to be cadmiun sulfide. It is extremely fine grained with a branching coral-like structure at the highest magnifications. This is only the second report of greenockite in Nova Scotia. Cadmium and zinc are chemically similar and often found in the same deposits.

Hemimorphite - Zn₄Si₂O₇(OH)₂·H₂O

This species was first visually identified by Terry Collett. It is the first report of the species at this locality and only the second report from Nova Scotia. It forms colorless to white transparent crystals in small coarse tufts. Identification was confirmed by Raman spectroscopy in 2013 by Don Doell, courtesy of the University of Arizona.

Hydrozincite - Zn₅(CO₃)₂(OH)₆

The most conspicuous mineral at this locality is hydrozincite. Generally, it forms thin powdery coatings on the rock. Rare pockets may have thick rich coatings of the mineral, as shown below. It is blue-white to brilliant white and fluoresces very brightly blue-white. This is one of only two locations in Nova Scotia where the species has been found (according to the Mineral Occurrence Database).

Smithsonite - ZnCO₃

This species was first visually identified by Terry Collett. It is the first report of this mineral at this locality and, to my knowledge, in Nova Scotia. It forms thin rough coatings on calcite. Worldwide, smithsonite can take on almost any color; at this location it is beige or tan. In general, smithsonite crystals are rare and none are known from this locality. Identification was confirmed by Raman spectroscopy in 2013 by Don Doell, courtesy of the University of Arizona.

Sphalerite - ZnS

Sphalerite forms druses of tiny crystals. They are a dark reddish-brown in color, but in the hand appear black. The thin veins that it forms in are often overgrown with calcite.

Unknown 1

This unknown mineral forms very thin tapering needles.

Conclusions

This is an interesting location for some unusual zinc secondary minerals for the region. It is the first locality in Nova Scotia for smithsonite and only the second for hemimorphite and greenockite.

Acknowledgements

Thanks to the excellent eye of Terry Collett, who spotted the smithsonite, hemimorphite, greenockite, and the unknown. Also thanks to Don Doell and U. Arizona RRUFF for the hemimorphite and smithsonite confirmations, and to Xiang Yang and Saint Mary's University for the greenockite analysis.

References

Nova Scotia Dept. Natural Resources, Mineral Occurrence Database.

Takahashi, T. (1960) Supergene alteration of zinc and lead deposits in limestone. Economic Geology: 55(6): 1083–1115.

Disclaimer: This page is intended for information purposes only. The locality is not necessarily open to collecting. The locality is not necessarily safe.