Introduction
While the rock at Ross Creek itself is North Mountain basalt, to either side of it are exposures of the McCoy Brook formation. The rocks of interest are sedimentary rocks that formed on top of the North Mountain formation. Several coves near Ross Creek are popular with beachgoers as the source of jasper and amethyst.
Geology
The McCoy Brook Formation is a geological formation dating to roughly between 200 and 190 million years ago. Originally, the southern exposures of the formation were treated as a distinct formation called the Scots Bay formation. It was discovered in 1894 by Ells and further described by Haycock (1900) and Powers (1916). It was formally combined with the McCoy Brook formation only in 1996 (Tanner). The 'Scots Bay formation' is only about 9 m thick, compared to the on-land thickness of the McCoy Brook formation of about 230 m. Hassan (2018) describes the rocks near Ross Creek (i.e. the Scots Bay formation) as:
Lithologically, the Scots Bay Formation is dominated by clastic sediments, including sandstone, silty sandstone, conglomeratic sandstone, and shale. Carbonate and silicified carbonate rocks include calcareous sandstone, packstone, mudstone, wackestone, and stromatolitic limestone.
The photo below shows a portion of the McCoy Brook formation at Lime Cove, showing fossils of what is believed to be silicified tufa-coated logs. This was a mineral-rich hot spring near the edge of a lake. The trees became covered in tufa. Later, the material was silicified forming agate/jasper. Occasionally, they have hollow centers lined with quartz that can be purple amethyst or dark smoky. A rare example from this location, now at Acadia University, showed branches and cones. Olsen's description is, "Abundant silicified tufa-coated logs. The logs are almost always completely gone, with the resulting cavity filled with botryoidal quartz and sometimes a geopetal fabric." Many locals refer to these as petrified logs, however petrification preserves the cellular structure of the wood which was not the case here.
Mineralogy
Most of the published literature is focused on the fossils. I am not aware of any comprehensive list of mineral species found at any of these sites. Birney De Wet and Hubert (1989) do mention heulandite, calcite, celadonite. They also describe microscopic goethite sprays and hematite in the japser.
Table 1: Minerals reported from Ross Creek (McCoy Brook formation)
Calcite - CaCO3
Calcite is found throughout the formation, generally as smaller crystals of little interest to collectors.
Laumontite - CaAl2Si4O12·4(H2O)
The specimen shown below was one of the earliest that I collected. It was found east of Ross Creek in a fractured sandstone or limestone and is associated with calcite.
Malachite - Cu2(CO3)(OH)2
Malachite was found east of Broad Cove near Ross Creek in vertical cracks in the rock (i.e. perpendicular to layering). They are flat, due to the limited space for development, but it is a sign that copper minerals are in the area.
Quartz - SiO2
Amethyst and smoky quartz are often found near Ross Creek. The source of the radiation, needed to color the smoky quartz, has long interested me, as these are not like the radioactive granite rocks of, say, Bayer's Lake. However, I have a gmelinite crystal from Amethyst Cove that is fluorescent due to uranium, and the hydrothermal fluids that created some of the zeolites would have been the same fluids that seeped into the McCoy Brook formation.
Stilbite - NaCa4Al8Si28O72·30(H2O)
An orange mineral was found east of Broad Cove, having formed in cracks in the rocks. It has a radial structure, but the cracks confined the development. It has the color and appearance of stilbite, and given that laumontite is also found in these rocks, another zeolite does not seem to be unusual.
Unknown 1
An unknown mineral was found associated with malachite near Ross Creek. It has a metallic luster and seems to form threads in ribbons or bundles in calcite. Presumably it is a copper mineral but based on the appearance, I don't have a good guess as to what it might be.
Conclusions
The minerals of the McCoy Brook formation have never been fully catalogued. While the Ross Creek quartz is well known, there are small amounts of other interesting minerals and further investigation may turn up new finds.
Acknowledgements
Thanks to Tim Fedak and the Nova Scotia Museum of Natural History for allowing me to photograph and share the smoky quartz image.
References
Birney De Wet, C.C. and Hubert, J.F. (1989) The Scots Bay formation, Nova Scotia, a Jurassic carbonate lake with Silica-rich hydrothermal springs. Sedimentology: 36: 857-873.
Ells, R.W. (1894) Notes on recent sedimentary formations on the Bay of Fundy coast. Transactions of the Nova Scotia Institute of Science: 416-419.
Hassan, H.S. and Othman, M. (2018) Petrology and Origin of Cherts in early Jurassic Scots Bay Formation, Nova Scotia, Canada. 2nd Annual Conference on Theories and Applications of Basic and Biosciences.
Hassan, Hassan Salem (2000) Sedimentology and paleontology of the lower Jurassic Scots Bay Formation, Bay of Fundy, Nova Scotia, Canada. Master of Science thesis, Acadia University, Wolfville, Nova Scotia.
Haycock, Ernest (1900) Records of Post-Triassic changes in Kings County, Nova Scotia. Transactions of the Nova Scotia Institute of Science: 287-302.
Olsen, P.E., Schlische, R.W., and Gore, P.J.W. (1989) Tectonic, depositional, and paleoecological history of early Mesozoic rift basins, eastern North America. Guidebook to International Geological Congress Field Trip T-351, 174 p.
Pe-Piper, G. (2000) Mode of occurrence, chemical variation and genesis of mordenite and other associated zeolites from Morden, Nova Scotia. Canadian Mineralogist: 38: 1215-1232.
Powers, Sidney (1916) The Acadian Triassic. Part 2. Journal of Geology: 24(2): 105-122.
Schenk, P.E., Rogers, D., Dalhousie Univ.: Depositional environment and chert formation in the lacustrine Scots Bay Formation, Triassic, Nova Scotia, 1970-72; M. Sc. thesis (Rogers). Stratigraphy and sedimentology of a Triassic lake and the diagenetic formation of chert nodules. Tanner, Lawrence H. (1996) Formal definition of the Lower Jurassic McCoy Brook Formation, Fundy Rift Basin, eastern Canada. Atlantic Geology: 32: 127-135.
Wallace, P. (1998) Ross Creek. in Discovering Rocks, Minerals, and Fossils in Atlantic Canada: A Geology Field Guide to Selected Sites in NF, NS, PEI, and NB. Atlantic Geoscience Society Special Publications, 87-89.
Disclaimer: This page is intended for information purposes only. The locality is not necessarily open to collecting. The locality is not necessarily safe.