Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (1)

These intriguing star-shaped or sun-shaped patterns found in boulders on the beach at Lyme Regis in Dorset are not fossils. At first glance, the distinct and clear designs look very much as if they would be. They are found in rounded boulders 60 – 90 cm across and are similar in size to the many large fossil ammonites that lie embedded in rocks all over the shore.

I thought when I originally discovered some, many years ago, that they looked like giant fossil starfish or jellyfish but knew that was impossible. The dark, roughly textured, radiating and circular lines of each pattern contrast with the smoother, paler rock in which they occur. The details of the patterns are different in each example. The patterns only seem to occur in slightly flattened boulders with an approximately rounded outline.

The patterns occur naturally in the boulders as a result of a geological process that I admit I do not fully understand. As far as I can make out, these sunstar-patterned boulders are calcareous concretions called Birchi Nodules that have fallen from strata high in the cliff that backs onto the seashore. They originate in a layer called the Birchi Nodular Bed on top of the stratum known as Shales-with-Beef. They are encased by a fibrous type of calcite known as ‘beef’. It is the ‘beef’ that forms the patterns in the outer layer of the nodule. The rocks date from the Lower Sinemurian of the Lower Lias in the Jurassic Period of about 190 to 200 million years ago.

To learn more about Birchi Nodules and Shales-with-Beef, I recommend that you refer to Lyme Regis – East to Charmouth, from Geology of the Wessex Coast of Southern England by Ian West, which is an extensive discussion of the geology of Lyme Regis in an on-line guide. This internet site is a virtual mine of local geological information to a fairly high level of complexity, with extensive referencing and illustration with photographs, diagrams, and maps both ancient and modern. 

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (2)

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (3)

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (4)

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (5)

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (6)

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (7)

Sunstar stone (with walking stick to show scale) at Lyme Regis, Dorset, UK, on the Jurassic Coast (8)

Sunstar stone amongst the other boulders on Monmouth Beach at Lyme Regis, Dorset, UK, on the Jurassic Coast (9) 

Revision of a post first published 3 May 2010

COPYRIGHT JESSICA WINDER 2011

All Rights Reserved

6 Replies to “Stone Sunstars at Lyme Regis”

  1. How intriguing indeed, I especially like the second photo where seaweed/lichen has embedded itself into the indentations on the right of the rock. Great stuff, Linda

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  2. Thanks, Linda. They are very strange phenomena. In fact, sunstar stones apparently have a habit of spontaneously disintegrating – which has led to accusations of vandalism on the beach. The green stuff in the crevices of the stone is just algal film. That particular picture was taken with 35 mm film ages ago and scanned.

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  3. They are odd structures, aren’t they? They disintegrate easily, too. People were being accused of vandalism at one time when it seemed as if they were being deliberately destroyed – but they just break apart naturally with weathering.

    Thank you for your concern. Everything is fine, thank you. I have in fact been posting something on the blog everyday. I wonder why you have not been able to access all the posts. However, some of the articles are revisions of earlier postings (like this one about the stone sunstars) rather than new pictures and information. I must get around to writing some new posts. I have been out and about a lot this summer taking thousands of photographs and short video clips on the seashore and elsewhere – and have no shortage of material – just a shortage of time.

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