Introduction
The locality of Clarke Head (sometimes spelled Clark Head) is located east of Parrsboro along the Minas Basin, in Cumberland County, Nova Scotia. It is a nice stretch of beach for a walk on a summer day. A variety of rock types and the results of a variety of geological processes can be seen in the area. This article covers the shoreline to the western side of Swan Creek, with the exception of the basalt, which is included in the Wasson's Bluff page. Of particular mineralogical note are several chlorine-rich minerals including marialite, chlorapatite, and potassic-chloro-hastingsite. It is also only the second Canadian occurrence of vésigniéite.
There are many cottages on top of the Head, so visitors should respect property and keep roadways clear.
Geology
Clarke Head is a geologist's playground. The area is shot through with numerous faults and a wide variety of rocks. Rock types present in the area include marble, quartzite, gabbro, limestone, hornfels, basalt, gneiss, sandstone and more. The locality has been described as a geological melange and a megabreccia.
The map below is included as a starting point, to show some of the different areas, but it is in error at least along the northern side of the head. There, much of the low cliffs are North Mountain basalt. Towards the mouth of Swan Creek (northwestern part of the map area), Blomidon Formation sandstone is exposed. At the time, it was thought to be McCoy Brook Formation but Calder et al. (2015) assigned the sandstone to the Blomidon formation and surmised that a fault must be present in the vicinity of the creek. The sandstone has produced some beautiful (micro) secondary copper mineralization.
Members of the Mesozoic Fundy Group (North Mountain and Blomidon Formations) are separated from the remaining rock by a continuous fault. The basalt on the north side of the Head ranges from hard columnar to brecciated and quite soft. Near the tip of the Head white gypsum is common and in places veins of vibrant orange gypsum var. satin spar. It is unclear what is meant by Bromley's designation of the Clarke Head Fault Zone. Though surely described in his text, I have not yet read it in full. This section of shoreline is not very exciting from a mineral collector's standpoint, although small hematite crystals are common.
A prominant seastack is found at some distance from the tip of the Head, which Bromley describes as gabbro, and represents an intrusive body. This seastack was the focus of a paper by Owen, although the paper mistakenly states that the seastack is at McKay Head, which is several kilometers to the east. The base is shot through with numerous veins described as a scapolite pegmatite.
A little to the west of the large seastack in a clast of what was originally described as gneiss, but in more recent papers is called granulite. The clast is about 10 m in size and located near the top of the cliff. Fragments from it can be found on the beach. They weather to an attractive white and black, finely striped surface. Gibbons and Murphy studied the boulder in detail. It contains orthopyroxene (enstatite), clinopyroxene (diopside), andesine, magnetite, ilmentite, garnet, biotite, and amphibole.
Although not shown on the map here, Bromley also mapped the rock exposed at low tide. A large fault extends roughly parallel to the shoreline for most of the map area. Between the fault and the shoreline is a strip of undivided Early Paleozoic-age rock.
The rock below is very interesting. This piece was found at the eastern end of Clarke Head and a larger piece was found far to the west, even west of the seastack. It appears to be a dark gray rock that has been bleached by some alteration. The rock is very fine grained. Notice that there are fractures running through the paler regions. Also, perpendicular to the fractures are numerous bluish-gray crystals that seem to be oriented perpendicular to the fractures. Those crystals are currently an unidentified species, but they are being investigated. The rock also contains tiny brassy-brown pyrite crystals.
Mineralogy
Minerals found include gypsum, pyrite, hematite, and silt pseudomorphs of halite. The amphibole hastingsite is also reported. At the seastack an unusual amalgamation of minerals can be found including analcime, hematite, rutile, titanite, epidote, magnetite, and chlorapatite. The seastack rock is pockety and could have produced some nice specimens, except that the minerals tend to be very intergrown resulting in a messy appearance. Coste (1888) reports prehnite from Clarke Head, but I am doubtful. Ankerite is reported (Fletcher 1892), but using modern redefntions of the species it would undoubtedly now be considered iron-rich dolomite. True ankerite is now exceedingly rare (see http://www.mindat.org/mesg-7-353729.html ).
In the 2000s a boulder of unusual gypsum produced some interesting micro crystals. There is a green mica (likely muscovite), crude pale green squarish prisms, tiny floater quartz crystals, tiny gemmy greenish-smoky brown floater tourmaline crystals, and very complex pyrite crystals. In a separate, more recent find, several copper minerals were found in sandstone including chrysocolla, cuprite, malachite, and vésigniéite.
Table 1: Minerals reported from Clarke Head.
Almandine - Fe2+3Al2(SiO4)3
Gibbons (1995) reports garnets in a granulite rock in the western portion of Clarke Head. The garnets are generally quite tiny (< 0.5 mm) though they can reach more than 1 cm in size. They are not likely to be of interest to collectors.
Analcime - NaAlSi2O6·H2O
This zeolite is an important constituant of the intrusive veins found at the seastack. While the aesthetics of the analcime are not great, they are well formed. Analcime is also associated with epidote in boulders behind the seastack. Analcime in Nova Scotia is best known from the North Mountain formation basalt, making this occurrence, which is not part that formation, different and interesting in that respect. The associated minerals also make for interesting specimens.
Baryte - BaSO4
Baryte has been found sparingly in Blomidon Formation siltstones near Swan Creek, associated with calcite and copper minerals. It forms tiny thin diamond-shape plates. The veins it forms in are thin and cut perpendicular to the bedding of the rock. Baryte is also found in the North Mountain basalt, not far away, where it is associated with chabazite; that occurrence is discussed on the Wasson Bluff page.
Calcite - CaCO3
Calcite is common along the shore, but good crystals are uncommon. Some interesting specimens have been found at the western end of the head, in fine grained sandstone to siltstone. The form consists of a negative rhomb {01·1} combined in roughly equal amounts with the {21·1} scalenohedron.
Chlorapatite - Ca5(PO4)3Cl
Chlorapatite forms sharp pseudomorphs after an unknown mineral at the seastack. The examples I've seen are in nearly 100% green mica. The original mineral formed rectangular prisms. The chlorapatite is white and forms radial sprays. Countless tiny sprays make up each of the original crystals. A few scattered flakes of mica and metallic crystals (pyrite?) are also in the pseudomorphs but may have been in the original mineral as well. The pseudomorphs are are very sharp and faithful. The chlorapatite was identified using qualitative EDS and is the first report of this mineral from Nova Scotia that I am aware of.
Chrysocolla - Cu2-xAlx(H2-xSiO5)(OH)4·n(H2O), x<1
Chrysocolla is found in Blomidon Formation siltstone close to the boundary with the basalt at Swan Creek. Most of the chrysocolla forms a very thin coating over calcite and chalcocite(?), where the coating is cracked and curled away from the surface like weathered paint. The example below is an exception. Chrysocolla should not form dendritic structures like that on its own, but copper is well know to branch, so it may be a pseudomorph after native copper.
Cuprite - Cu2O
Found in small amounts at Swan Creek, in Blomidon Formation siltstone, associated with other copper secondary minerals.
Dolomite - CaMg(CO3)3
White rhombs that do not effervesce in acid (i.e. not calcite) are common. They are likely dolomite, but I have not have them tested. The photo below shows some crystals that have weathered from massive gypsum. The rhombic shap can be seen in the cluster at lower left. There are dirty-orange crystals visible in some of the other iron-rich rocks. Presumably those are the reported ankerite. Redefinitions of ankerite and dolomite in recent years now mean that true ankerite is very rare and that the previously reported ankerites would now be considered iron-rich dolomite.
Dravite (Tourmaline) - NaMg3Al6(Si6O18(BO3)3(OH)4
As noted elsewhere a gypsum boulder was found with many unusual minerals in it. One of the minerals is olive green to brownish in color, very gemmy, and forms very sharp floater crystals less than 1 mm in size. They are trigonal and complex in shape. They were first visuallyidentified as tourmaline. Later, Raman testing confirmed that they are a tourmaline. Finally, in 2021 EDS was performed and magnesium was found to be dominant over iron, indicating that they are dravite.
Authigenic (i.e. formed in this rock rather than being transported here) tourmaline is known from evaporite deposits (Henry and Dutrow, 2012). The essential boron is derived from the evaporites themselves; certainly Nova Scotia has other borate minerals in gypsum/anhydrite suggesting that locally high concentrations of boron were present when those rocks were forming. The perfection of these tourmaline and the quartz crystals suggests to me that they are authigenic.
Epidote - Ca2(Fe3+,Al)3(SiO4)3(OH)
Boulder surfaces covered with micro green crystals of epidote are found on the mainland opposite the seastack. The crystals are especially attractive under magnification. They are well formed and transparent. They are sometimes associated with analcime. Searching MinDat.org, this seems to be an unusual combination (at least for submitted photos), but it has been found in a few other places in the world.
Gypsum - CaSO4·2(H2O)
For descriptive purposes, gypsum has the varietal names of selenite for transparent blocky crystalline material and satin spar for material consisting of parallel fibers. Micro crystals of the selenite variety are sometimes found here but more conspicuous are the veins of bright orange satin spar. Some massive gypsum boulders that weathered out onto the beach have hosted other minerals, including hematite, mica, quartz, and tourmaline.
Hematite - Fe2O3
Hematite is common as flakes and thin tabluar to platey crystals. It is common in the sedimentary rocks, although nearly always the crytals are frost damaged. Occasionally, nice micro crystals can be found. Better, thick crystals have been obtained from the seastack, from pockets or by etching away encasing calcite.
Ilmenite - Fe2+TiO3
Ilmenite is reported from the granulite rock (Gibbons et al 1996).
Magnetite - Fe3+2Fe2+O4
A specimen given to me by Terry Collett identified an unknown black octahedron. The octahedron separated from the matrix and it was attracted to a magnet. Based on the magnetic property, habit, and color, magnetite is a reasonable guess. Magnetite is reported from the granulite rock (Gibbons et al 1996).
Malachite - Cu2(CO3)(OH)2
Some fabulous malachite sprays were found in a small find of copper-secondaries at Swan Creek. They formed these more open sprays of very rich darker green crystals (see photo below), and tighter balls of lighter green malachite.
Marialite (Scapolite) - Na4Al3Si9O24Cl
The rock at the base of the seastack contains high proportion of scapolite. It is high in sodium and chloride making it marialite rather than meionite. Owens makes the reasonable assumption that the Na and Cl are derived from underlying evaporite rocks such as halite. Halite is found in commercial deposits at Nappan and Pugwash to the north. Owens reports finding scapolite crystals up to 20 cm in length, though most are considerably smaller.
Muscovite - KAl2(AlSi3O10)(OH)2
In 2004, Terry Collett, Doug Wilson, and I found a gypsum boulder on the beach that contained some interesting minerals, including tiny floater quartz crystals, complex pyrite, tourmaline, etc. It also contained pale green square prisms to several millimeters in length. The prisms consist of a flaky mineral, which was qualitatively identified as muscovite. So, because of the shape, the structures must be pseudomorphs of muscovite after some unknown mineral. These were common in the boulder.
Also in the boulder were nice hexagonal flakes with a rich deep green color. I am assuming that these are also muscovite, but they have not specifically been tested.
Potassic-chloro-hastingsite - {K}{Ca2}{Fe2+4Fe3+}(Al2Si6O22)(Cl,OH)2
The megabreccia zone, is found 1000 m from the campground stairs to the beach. "Hastingsitic" amphibole veins are reported cutting the "mylonitic granulite fabric" (Waldron et al. 2005). It is also stated that these are the most Cl-rich amphiboles yet reported. As such, until I have further information, I'm using the chemical formula for potassic-chloro-hastingsite above, because it is the most chlorine-rich hastingsite. Also Oberti et al. (1993) write "it has long been known that all Cl-rich amphiboles are potassium hastingsite, rich in K and Fe2+.
Makino et al. (1993) note that the highest Cl content to that date was 7.24 wt.% and that high concentrations above 3.0 wt.% were reported from a few localities, but it seems to be rare. Giesting and Filiberto (2015) write that "Chloro-amphiboles (Cl > 1.0 apfu) are rare in the terrestrial setting." and "In some cases, chloro-amphibole is accompanied by other high-Cl silicate phases like marialitic scapolite" which agrees with the situation at Clarke Head. Other sources say that Cl has affinities for Fe and separates from Mg.
The veins at Clarke Head are figured in Gibbons et al. (1996) but chemical data is not given.
Pseudomorphs
Interesting mudstone pseudomorphs after halite have occassionally been found on the beach. They can be quite sharp and sometimes show the hoppered faces that are characteristic of halite.
There are also casts after another unknown mineral. The casts have oblique angles and are often filled with small selenite crystals.
A third type of pseudomorph is found in the seastack rocks. They are chlorapatite after an unknown mineral. See the chlorapatite section for more information.
Pyrite - FeS2
Good pyrite crystals can be found in a some of the silty layers. They form pyritohedrons generally accompanied by small cube faces. rarely, octahedral faces are also observed. The larger crystals tend to be flattened somewhat. Many crystals are striated produced from competition between the cube and pyritohedron forms. As well, many crystals are malformed, with somewhat cavernous faces.
In 2004 some very complex crystals were found in a gypsum boulder. These are quite tiny, perhaps in the range of 100 microns. The drawing below represents an ideal crystal as constructed by P. Richards who measured the crystal on a goniometer. He also made two notes about the crystal. Firstly, the {210} faces were uneven so they did not give a good reflection, but they were consistently present. Secondly, despite the unusually high indices of the {10 5 2} measured form, the fact that it is a bevelled edge between {210} and {211} makes it reasonable.
A few of the complex pyrites were imaged in an electron microscope. Two images are shown below of one crystal using the standard view and BSE. The model above was then oriented, and form strengths adjusted to match the SEM/BSE images. It was necessary to add in an extra form to improve the match. The model is still not perfect (the BSE image seems to show a few additional faces), but is close. The model is then rotated back to clinographic view. A very complex and interesting crystal!
Quartz - SiO2
Henry How (Mineralogy of Nova Scotia, pg 203) lists pseudomorphs of quartz after stilbite. Nothing more is said about them and to my knowledge none have been found in recent years or survived from those early finds.
I have seen tiny (approx 1 mm) perfectly transparent floater quartz crystals in massive gypsum matrix.
Rutile - TiO2
Reported from the seastack.
Titanite - CaTiSiO5
Yellow to greenish yellow, lustrous crystals of titanite are found at the seastack. They are associated with analcime, green mica, scapolite, and hematite. They can reach up to 1 cm in size.
Vésigniéite - BaCu3(VO4)2(OH)2
In the whole of Canada, this species was previously only found once in Prince Edward Island, in a drill core made in sedimentary rock during the search for uranium (Bottrill et al. 1969). In this new occurrence it was found as tiny blebs associated with (though not intimately) copper secondary minerals at Swan Creek. Though without crystal form, they stand out visually due to a yellow-green color that is unlike any other minerals from Nova Scotia. An analysis using WDS showing the mineral contained barium, vanadium, and copper. This is the only mineral with all three of those elements. In addition the color and environment are matches to that species. This is the first vanadium mineral found in Nova Scotia. It is worth noting that vanadium is also the cause of the green color that is sometimes seen in apophyllite (Rossman 1974) and that many apophyllites in Nova Scotia are green.
Unknown 1
Black, often lustrous, prismatic crystals, striated along their length, up to a few millimeters in size. Likely a copper sulfide such as chalcoite, digenite, or djurleite but a realiable ID will require single crystal XRD as powdering for powder XRD can alter from one phase to another. These crystals are found on calcite with chrysocolla, malachite, cuprite, barite, etc. in siltstones of the Blomidon Formations at Swan Creek, in thin crossbedding fractures.
Unknown 2
Though they are flat and only consist of broken surfaces, these are very large (10-20 cm) crystals of a beige mineral. Associated with hastingsite on fracture surfaces of granulite.
Unknown 3
Bluish-gray elongated crystals found it what appears to be an altered and bleached fine grained rock (see geology section). They don't seem to have well defined faces and are soft and flaky. Possibly pseudomorphs.
Conclusion
Clarke Head is a great place for a walk on a summer's day. Even over a relatively small distance the geology is quite varied with basalt, gypsum, other sedimentary rocks, and igneous intrusive bodies. Don't expect great specimens, but there are some interesting microcrystals.
Acknowledgements
Thanks to Dick McAllister for the use of the halite pseudomorph image and for bringing to my attention the proper location of the seastack; to Dino Nardini for use of the seastack image; and to Terry Collett for the gift of his Clarke Head reference collection. Also thanks to Xiang Yang and Saint Mary's University for the dravite EDS analysis.
References
Bromley, M.H. (1987) Geology of the melange at Clarke Head, Cumberland County, Nova Scotia. Bachelor of Science Thesis, Acadia University.
Bottrill, T.J., Prest, V.K., Steacy, H.R. (1969) Occurrences of Uranium and Vanadium in Prince Edward Island. Geological Survey of Canada, Paper 68-74: 14 pgs.
Calder, J.H., Naylor, R.D., Waldron, J.W.F., Adams, K., Fedak, T., George, E., Giles, P.S., Stevens, R. (2015) Geological Mapping at Parrsboro (Cape Sharp to McKay Head), Nova Scotia. Nova Scotia Department of Natural Resources, Geoscience and Mines Branch, Report ME 2015-001, Report of Activities 2014.
Coste, E. (1888) Report on the mining & mineral statistics of Canada for the year 1887. Geological Survey Canada, Annual Report (New Series), vol. 3 part 2. [Online 2017]
Fletcher, H. (1892) Geological Survey of Canada, Annual Report vol. 5, (1890-91), pt. P, 101P. [Online 2017]
Gibbons, W. and Murphy, J.B. (1995) Mylonitic mafic granulite in fault megabreccia at Clarke Head, Nova Scotia: a sample of Avalonian lower crust? Geological Magazine, 132.
Gibbons, W., Doig, R., Gordon, T., Murphy B., Reynolds, P., White, J.C. (1996) Mylonite to megabreccia: Tracking fault events within a transcurrent terrane boundary in Nova Scotia, Canada. Geology, 24(5), 411-414.
Giesting, P.A., Filiberto, J. (2015) Crystal chemistry and formation mechanisms of the potassic-chloro-hastingsite in MIL03346 and paired stones. 46th Lunar and Planetary Science Conference. 2396.pdf.
Henry, D.J., and Dutrow, B. (2012) Tourmaline at diagenetic to low-grade metamorphic conditions: Its petrologic applicability. Lithos, vol. 154, pg. 16-32. [Online 2017]
How, H. (1869) The Mineralogy of Nova Scotia. A Report to the Provincial Government. Charles Annand (Publisher), Halifax, Nova Scotia. [Online 2017]
Makino, K., Tomita, K., Suwa, K. (1993) Effect of chlorine on the crystal structure of a chlorine-rich hastingsite. Mineralogical Magazine, 57, 677-685.
Oberti, R., Ungaretti, L., Cannillo, E., Hawthorne, F.C. (1993) The mechanism of Cl incorporation in amphibole. American Mineralogist, 78, 746-752.
Owen, J.V. and Greenough, J.D. (1999) Scapolite Pegmatite from the Minas Fault, Nova Scotia. Mineralogical Magazine, vol. 63, no. 3, pp. 387-397. [Online 2017].
Waldron, J.W.F., White, J.C., MacInnes, E., Roselli, C.G. (2005) Field TripB7, Transpression and transtension along a continental transform fault: Minas Fault Zone, Nova Scotia. Atlantic Geoscience Society, Special Publication Number 33. [Online 2020]
Disclaimer: This page is intended for information purposes only. The locality is not necessarily open to collecting. The locality is not necessarily safe.