Rock Texture & Pattern at White Point

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Without a four-wheel drive vehicle we couldn’t make it as far as the promontory called White Point along the Cabot Trail in Cape Breton Island. We stopped instead at the harbour in the village. Here the walls and sea defences were made of large stacked boulders of the same local rock that outcrops at the Point so it was possible to get a really good look at the composition of them. It was amazing. It was a sunny day and everything sparkled. The rocks themselves actually sparkled. I couldn’t believe my eyes. Even the sand and the waves sparkled. I tried desperately to capture the magic of it but it was difficult because the camera mostly over compensated for the bright points of light.

Close-up it was possible to see that the rocks had large plate-like crystals of transparent mica minerals (muscovite) which were acting as small mirrors. The sand had an abundance of these shiny crystals weathered out of the rocks and catching the light. The waves agitated the crystals and further  increased the sparkling effect.

The rocks are a mixture of pink granitic gneiss and silvery black biotite schist. They originated as intrusive molten magmas beneath the earth’s crust in Devonian times approximately 375 million years ago, forming a large mass called a pluton – specifically  the Black Brook Granitic Suite. The igneous rock which has  been metamorphosed to black biotite schist was the first to be deposited and compressed into rough layers or foliations with a parallel alignment of the crystals. The igneous rock which is now mainly granitic gneiss intruded into the schist preferentially along the lines made by the foliations. There are also veins of aplite and pegmatite. The alternation of these two rock types is a wonder to behold on White Point itself. My photographs have focussed on details of the patterns and textures as revealed by the rip-rap boulders in the nearby harbour.

REFERENCES

Anoiyothin, W.Y. and Barr, S.M. (1991) Petrology of the Black Brook Granitic Suite, Cape Breton Island, Nova Scotia. Canadian Minerologist, Vol. 29, pp. 499-515.

Barr, S.M. and Pride, C.R. (1986) Petrogenesis of two contrasting Devonian Granitic Plutons, Cape Breton Island, Nova Scotia. Canadian Minerologist, Vol.. 24, pp. 137-146.

Donohoe, H. V. Jnr, White, C. E., Raeside, R. P. and Fisher, B. E, (2005) Geological Highway Map of Nova Scotia, Third Edition. Atlantic Geoscience Society Special Publication #1.

Hickman Hild, M. and Barr, S. M. (2015) Geology of Nova Scotia, A Field Guide, Touring through time at 48 scenic sites, Boulder Publications, Portugal Cove-St. Philip’s, Newfoundland and Labrador. ISBN 978-1-927099-43-8, pp. 94-97.

Atlantic Geoscience Society (2001) The Last Billion Years – A Geological History of the Maritime Provinces of Canada, Atlantic Geoscience Society Special Publication No. 15, Nimbus Publishing, ISBN 1-55109-351-0.

7 Replies to “Rock Texture & Pattern at White Point”

  1. I wish I could find similar sources for European rocks. I keep taking photos, wondering what they depict, not really knowing anything about geology.

  2. It is quite difficult isn’t it? It helps to know absolutely the location in which the photographs are taken. If it is in a National Park or a tourist area, then there might be leaflets or websites describing the geology. Internet searches using the location name plus rocks or geology may yield further descriptions and academic papers. Geology maps can be helpful too. The biggest problem is understanding the descriptions of the geology because it is a branch of science with a vocabulary all of its own. It can be good fun finding out and learning as you go along – which is what I am doing. I have a little bit of background with geology but not much – so most of what I say about the rocks I photograph is tentative and maybe a bit generalised.

  3. The terminology wouldn’t be a problem, I’m used to learning something new all the time. I’ll persevere… 🙂

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