Introduction

A large area of Cape Breton contains marble and serpentine rocks. They are generally of little interest to mineral collectors. The Scotch Lake Quarry, however, exposes a considerable amount of rock and there are small amounts of interesting microminerals. This quarry is excavated out of the side of the Boisdale Hills, about 17 km northwest of Sydney River in Cape Breton County. It is readily visible from the road.

History

Parks writes, in 1912, about the property then owned by the Dominion Coal and Steel Company,

"The quarry is connected by a spur with the Intercolonial Railway at Scotch Lake, and is equipped with a modern quarrying and crushing plant. Sixty-five men are employed and about 300 tons a day are shipped to the furnaces at Sydney. The quarry is operated under contract for the owners by Mr. Wm. Routledge, who also performs similar work for the Nova Scotia Coal and Steel Co. on the adjoining property to the east."

Sabina reported that it was worked for about 50 years until 1951 for dolomite. The dolomite was used as flux at the Dominian Steel and Coal Corporation in Sydney. The quarry was also worked in the 1960s for aggregate. The locality is also referred to as the George/Georges River Quarry.

Geology

The main mineral of interest in the operating quarry was dolomite. Limestone was also quarried nearby, prior to the development of the main quarry. The dolomite was altered to varying degrees to serpentine. Moderately altered rock is yellow and severely altered rock is a deep green. Milligan reports that the severely altered material has the smooth greasy feel of talc, which is a secondary alteration product.

Mineralogy

The minerals listed by Sabina include: serpentine, calcite, pyroaurite, tremolite, talc, magnetite, hematite, pyrite, graphite and dolomite. It is not clear when these, in particular the pyroaurite, were first identified. She lists only one reference (Parks), but it does not mention pyroaurite. Perhaps she identified it from material she collected. The provincial museum has a specimen labelled as chromite; again I don't know how the identification was made. Celestite, pectolite, apophyllite, and aegirine were identified recently using Raman spectroscopy, and fluorite in 2021 by EDS. Finally, Felderhof (1978) lists an earlier report by Campbell and Shea (1957, itself a second hand report) of barite from the locality. None of the later reports were able to verify the occurrence.

With some careful investigation, it wouldn't surprise me that additional minerals could be found at the locality.

Table 1: Minerals reported from Scotch Lake Quarry, Nova Scotia.

Aegirine - NaFe³⁺Si₂O₆

A pod of pectolite, about 15-20 cm in diameter, was found with aegirine crystals on the pectolite. Identification was made using Raman in 2018. Though the crystals appear black, fragments and thinner crystals show the green color under magnification and good lighting. This rules out the similar mineral arfvedsonite. The maximum crystal size was about 8 mm in length by 1-2 mm in diameter. All but the tiniest crystals were broken and without terminations. I believe this is the first report of the mineral from this location.

Brucite - Mg(OH)₂

Blue-green / turquoise colored plates are often found on or embedded in calcite, or on fluorite. Some exhibit trigonal or hexagonal outlines. They are transarent/translucent, soft, and micaceous. EDS shows only magnesium and oxygen, suggesting brucite. That species determination agrees with the visual/physical characteristics and the environment.

Calcite - CaCO₃

Calcite is a common mineral, forming micro crystals lining small vugs and veins. The crystals tend to be blocky and they are fluorescent. Otherwise they are not particularly interesting. I've also collected very tiny, white sprays on calcite, as shown below. When EDS is performed, however, the small crystals also come back as calcite. So, that specimen represents two generations of calcite of different habits.

Chromite - Fe²⁺Cr³⁺₂O₄

The Nova Scotia Museum of Natural History has a specimen (catalog number 967GM0193.026) labelled as chromite. There is no indication how the identification was made, though the side of the specimen is sliced away suggesting a piece was taken for analysis. Two views of the specimen are shown below. It is 5x5 cm and consists of a rough mixture of chromite and a white mineral. The chromite is dark gray to black on the exterior surface and yellow-brown on the cut surface. This is the first report of chromite from Nova Scotia. The label indicates the specimen was collected in 1915, so it was found fairly early in the mine lifetime.

Fluorite - CaF₂

Fluorite seems to be rare at Scotch Lake. I've only seen it once as lumpy pale purple druses. On that specimen, bluish-green micaceous brucite has formed over some areas of the purple mineral. That material was found in 2020 and EDS wrk done in 2021.

Graphite - C

From one boulder we collected a large number of small blebs of a black mineral. The mineral is poorly formed, though it appears to be somewhat flaky in appearance. One crystal appeared to have a hexagonal outline, but that may be my bias. It occurs on and in calcite. It seems to be flexible and the streak is black. These qualitative tests, combined with the list of known minerals, suggests graphite.

Magnesite - MgCO₃

I also have a specimen showing an oriented white fibrous mineral over a surface of serpentine.

Magnetite - Fe²⁺Fe³⁺₂O₄

Beautiful micro magnetites are somewhat common. They are razor sharp and quite lustrous. The form is a pure octahedron with no visible modifying forms. They are found on calcite crystal druses.

Pectolite - NaCa₂(HSi₃O₉)

A single specimen has been found with a pod of pectolite about 15-20 cm across. White pectolite lined the pod, with a distinct but not sharp boundary with the surrounding rock. The interior of the pod was open, with the pectolite crystals arranged somewhat radially in the pod but intergrown into a very tough material. Minerals found on the pectolite include aegirine and small amounts of calcite and a mica. Sadly, nearly none of the pectolite crystals are terminated.

Although I have a specimen of pectolite from an unknown locality closer to Parrsboro, this is the first pectolite that I am aware of from a known Nova Scotian locality.

Pyroaurite - Mg₆Fe³⁺₂(CO₃)(OH)₁₆·4H₂O

This is a fairly rare mineral worldwide. It is listed in Sabina, but she reports it as a 'blue translucent coating with fibrous structure'. Recent collecting has turned up crystals that are quite different looking. They are opaque with a matte luster, orange, trigonal, and blocky to tabular, reaching about 1mm in size, and are found on calcite. They are very attractive and very fine for the species. A review of the MinDat database suggests they are only surpassed in quality by the enormous crystals from the famous Langban deposit in Sweden, which also happens to be the type locality for the mineral. This material was confirmed by Raman and single crystal XRD (RUFF Project ID R120011).

Serpentine Group - D₂[Si₂O₅](OH)₄

Green massive serpentine is the most common and conspicuous mineral at this locality. It comes in various shades from yellow-green to deep green. Red, blue and brown specimens are also reported. I have heard that it carves very well, but have not seen any finished objects. Serpentine is a rather large group of minerals, but one EDS analysis showed this green material to be magnesium dominant. There are still three Mg serpentines, but lizardite, Mg₂[Si₂O₅](OH)₄ is the most common (volumetrically) serpentine species and appears to be a good fit.

Talc - Mg₃(Si₄O₁₀)(OH)₂

Though reported, the nature of these two minerals is unknown. The only reference I can find is MacDonald (1992) who writes that "thin layers of talc are found along some shear zones in the serpentized dolomite." I have a specimen of a white mineral from a shear zone that visually could pass for talc - and it is soft. When it was analyzed by EDS is showed both Mg and Si, which also agrees with talc.

Tremolite - Ca₂Mg₅(Si₈O₂₂)(OH)₂

I have a specimen with a pod of massive pyrite and near the pyrite are small veinlets of a pale blue-gray fibrous mineral. It might be tremolite, based on the habit, but no testing has been performed. A photo is shown below.

Unknown 1

Small amounts of a colorless micaceous mineral were found with the aegirine on pectolite. They are flexible, but I was not able to determine if they are also elastic.

Unknown 2

This unknown consists of brilliant white crystal aggregates on calcite, in some areas forming a complete covering. The structure of the mineral is very hard to discern. A review of MinDat, using localities that similar mineralogy, suggests hydrotalcite and hydromagnesite are possibilities, but no testing has been performed to date. That material was found in 2020.

Conclusions

This quarry is easy to access, being very close to the road. There is a lot of rock around on the floor. Though pockets are rare and small, you can be rewarded with some interesting and attractive microminerals. The quarry has also produced specimens of species that are rare elsewhere in the province.

Acknowledgements

Thanks to Don Doell and Terry Collett for the pyroaurite specimen, and to Don for the Raman of the aegirine and pectolite. Thanks to Don Doell and the RUFF project for the pyroaurite, celestite, pectolite, apophyllite, and amphibole identifications. Also thanks to Deborah Skilliter and the Nova Scotia Museum of Natural History for allowing me to photograph the chromite specimen and share the picture. Finally thanks to Xiang Yang and SMU for several EDS analyses.

References

(to get) C.O Campbell and F.S Shea, "Barytes occurrences in Nova Scotia", N.S.D.M. map, 1957.

G.W. Felderhof, "Barite, Celestite and Fluorite in Nova Scotia", Nova Scotia Department of Natural Resources, Bulletin ME 4, 1978. [Online 2015]

R.H. MacDonald, "Various Industrial Mineral Commodities in Nova Scotia", Nova Scotia Department of Natural Resources, Mines and Energy Branches, Economic Geology Series 92-1, pg 62. [Online 2018]

G.C. Milligan, "Geology of the George River Series, Cape Breton, Stratigraphy, Structure, and Economic Geology", Nova Scotia Department of Mines, Memoir 7, 1970. [Online 2011]

W.A. Parks, "Report on the Building and Ornamental Stones of Canada", Vol. 2, Maritimes Provinces, Canada Department of Mines, Ottawa, 1914. [Online 2013]

A.P. Sabina, "Rocks and Minerals for the Collector, Northeastern Nova Scotia, Cape Breton Island, and Prince Edward Island", Geological Survey of Canada, 1994.

"The Mineral Province of Eastern Canada: Geology of Nova Scotia", Department of Mines, Nova Scotia, 23pp., 1953.

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