West, I.M. and Harvey, D. 2013. Lodestone, magnetite on the Chesil Beach: Geology of the Wessex Coast. Internet site: www.southampton.ac.uk/~imw/cheslode.htm. Version: 1st July 2013 updated, based on 6 February 2007 version.
Chesil Beach - Lodestone, Magnetite Pebbles

By Ian West,
Romsey, Hampshire
and Visiting Scientist at:
Faculty of Natural and Environmental Sciences,
Southampton University,

Website hosted by courtesy of Isolutions, Southampton University


Field Guide List | Home | Field Guide Maps and Introduction| Chesil Beach, general| Isle of Portland - Introduction|

magnetite pebbles on Chesil Beach

Dorothea on Chesil Beach

magnetite pebble


Chesil Beach and Portland Field Guides ---

Chesil Beach -Introduction Page
Chesil Beach - Magnetite Pebbles (lodestone) from a Shipwreck
Isle of Portland - General
Isle of Portland - Portland Bill
Isle of Portland - Withies Croft Quarry
Isle of Portland - Bibliography

Go back to top

Introduction

Magnetite pebble on the Chesil Beach

Angular magnetite pebble

Rectangular magnetite pebble

Magnetite pebbles were first discovered on the Chesil Beach in recent years by Mr David Harvey, who discovered black magnetic pebbles at the Abbotsbury end of the Chesil Beach in the year 2000. With them were other pebbles apparently of magnetite which seemed to have no major effect on a compass. Associated are some pebbles of metamorphic rock, such as schist or gneiss. Magnetite, also known as lodestone, is not a material that would be expected on the Chesil Beach and thus the possibility of a shipwreck origin was investigated.

Go back to top

Location

Location photo for the magnetite pebbles

The black magnetite pebbles occur at about the low water mark at about 1200m southeast of the end of the Fleet Lagoon. The map reference is SY 578832. The photograph shows Ian West standing near the crest of the beach lined up with the pebble location on the foreshore. If a line is taken normal to the beach and lagoon at this point and is entended seaward this will fix the position of the main concentration of pebbles on the beach. The hill beyond the Fleet Lagoon here is Chesters Hill (northwestern part). (Incidental points about the photograph: 1. A notable feature of the Fleet Lagoon is that there are no cliffs at the back of it, that is on the landward side, and this suggests that the Chesil Beach has always protected the land behind as sea-level has risen. This is very obvious at this point, Chesters Hill, where only some minor slumping is seen in the Forest Marble of flaggy limestone and shale. 2. Notice how plastic debris is washed and blown over the crest of the beach. The driftwood shows that the waves swash over the top in storms. 3. Notice how some low vegetation is being to colonise the flat crest of the beach.)

Go back to top

Magnetite - The Mineral

Magnetite, magnetic iron ore, or lodestone (loadstone) is iron oxide, Fe 3 O 4 . It contains 72.4 % iron so it is a valuable ore of iron. There can be some small amount of replacement of iron by magnesium or titanium in some cases. The mineral belongs to the cubic system and is commonly as octahedra. There is a poor octahedral cleavage. The colour is iron-black. The streak is black and the lustre metallic or submetallic. The hardness is 5.5 to 6.5 on the Moh's Scale and it is notably of high density so that when pure it has an SG of 5.18.

Magnetite occurs as a primary constituent of most igneous rocks and is often present as minute crystals. Large deposits are considered to be the result of magmatic segregation, as in the Urals, and Northern Sweden, Kiruna, Gellivaare etc. Workable magnetite deposits occur also in lenses in metamorphic rocks, such as schists, as in the Adirondack belt in the eastern U.S.A. The pre-metamorphic nature of these deposits is a matter for discussion. Pyrometasomatic and contact-metamorphic (i.e. skarn) magnetite deposits are widespread but not of great importance in production. Magnetite is a constituent of many veins; it is found in residual clays, and in placer deposits - the "black sands" - formed by the degradation of earlier deposits. For more information on the mineral see Magnetite: The Mineral and Gemstone Kingdom.

Lodestone is magnetic magnetite. In historic times it was used to magnetise the soft iron wire in a compass card suspended at the centre of a vertical needle. The ships had to carry lodestone to remagnetise this wire. See the website: Navigation: The Mariner's Magnetic Compass.

Without lodestone the Chinese would not have invented the magnetic compass and the great voyages of discovery could hardly have taken place. Not all magnetite is magnetic (and it is not all magnetic here on the Chesil Beach). Lightning strikes of magnetite are believed to cause the iron oxide to become magnetic. For more information on this see the website The Loadstone .

The Pole Star (Polaris) served as the seaman's lodestar (or star that shows the way). Therefore the magnetic stone which was used to magnetize the compass needle was called a lodestone. The magnetic, direction-finding property of the lodestone had been discovered in China as early as the twelfth century. By the sixteenth century, the mariner's compass was made with a soft iron wire bent to a lozenge shape and attached to the underside of a circular compass card, which was suspended at the center on an upright needle. Because the iron wire tended to lose its agnetism over a period of time, it was necessary for each ship to carry a good lodestone to re-magnetize the wire when it weakened.

Go back to top

The Magnetite Pebble Concentrations

Site of the magnetite pebbles at low tide

The beach in wet weather

These photographs are to provide an impression of the beach at low tide in wet weather on the 18th of October, 2000. The waves were of significant size, although not great for the Chesil Beach. The tide was low and the pebbles were easily found just over a kilometre from the end of the Fleet Lagoon. The beach changes and these pebbles may not be so clearly visible now. David Harvey and Ian West had walked southeast from the Dragon's Teeth (wartime concrete defences against German tanks) at Abbotsbury. Mr Harvey soon found some isolated pebbles, which led him to the main exposure rich in magnetite, which was already well-know to him. It is worth noting that there are also black chert pebbles on the beach, but of course are easily distinguished by conventional tests. The pebbles are mostly present in the wet lower part of the beach in the left photograph from the camera to the figure. The ones at my feet ( in the right photograph are fairly small, but numerous. There is also black magnetite sand, mixed in with brownish quartzose sand. Larger isolated magnetite pebbles (like those in the photographs with the compass) occur higher on the beach. They are scattered in this general area, but do not seem to be present at the top of the beach.

Go back to top

Source of the Iron Ore?

The source of the magnetite is a fascinating problem. The mineral does not occur in any significant quantity in the area, and the metamorphic rocks associated with it are not found near Dorset. It is true that the Chesil Beach contains material from southwest England, but any large source of magnetite there that could be naturally transported to this beach is not known. Quartzite pebbles like those of Budleigh Salterton are common in some parts of the Chesil Beach, but no large magnetite exposure has been found in east Devon, as far as the authors are aware. In any case, nearly all the Chesil Beach pebbles are of highly resistant, quartz-rich rocks and the magnetite is softer (hardness 5.5 to 6.5 on the Moh's Scale). Furthermore, the magnetite pebbles are very localised and not widely distributed along the beach. Natural processes do not easily account for this accumulation. Thus, a possible shipwreck source was kindly investigated at our request by Gordon Le Pard of the Dorset Coast Forum, Dorchester.

The Dorothea on the beach in a storm

The Dorothea stranded

Refloating of the Dorothea

Gordon Le Pard seached the Maritime Archaeological Record at Dorchester for a possible shipwreck which might have deposited the iron ore found on the Chesil Beach. He found that of the 141 wrecks that he has listed as having taken place on the Chesil Beach, only one is recorded as carrying iron ore. There may have been others, however, because for more than half the wrecks, the cargo is not recorded or is given as general or mixed cargo.

The one wreck that certainly carried iron ore, according to Gordon Le Pard, is that of the Dorothea, which ran on the beach between Abbotsbury and Langton Herring on the 14th February, 1914. The location is approximately right. He reported that the ship was eventually salvaged, but this would have entailed removing the cargo to lighten the vessel. He commented that it would not be surprising if a substantial amount of iron ore was spilt on the beach as the cargo was transhipped. Mr Le Pard has kindly provided the photographs, shown above, which have been reproduced with minor modificatin. Here are some further notes from Mr Le Pard's collection. "When the steamer Dorothea, of Rotterdam, went ashore at Langton during the night of 14th/15th February 1914, the crew were able to walk ashore at low water." ...."One which caused a good deal of interest locally was that of the Dorothea, a large coaster carrying iron ore from Spain to Holland, which in February 1913 (?) was carried broadside on high up the beach at Abbotsbury where she remained high and dry from months. At last, when she had been almost despaired of, she was refloated during an exceptionally favourable tide." Caption to the right-hand side photograph above. "The Salvage vessel Lyons standing by the S.S. Dorothea, stranded on Chesil Beach in February, 1914." Note by Mr Le Pard of recollection of Mr Walter Bellamy. "..Mr Bellamy rescued two dogs from the wreck in a pillowcase, a pom. and a daschund. At Abbotsbury the captain's wife saw rabbits and said "rabbits" - the only English word she knew! Mr Bellamy said that the cargo was left on board."

Notes by Gordon Le Pard from the Dorset Year Book, 1969-70, pp. 105-106. "The Salvaging of the Dorothea". The vessel was after a time launched broadside down the beach, a clever piece of work carried out by a firm from Great Yarmouth. Baulks of timber were placed under her keel to form "ways" for her to slide down on. When a tier of baulks had been laid, two of our tugs would start towing, one on the bow and one on stern; when far enough down they repeated the operation with baulks and so on until she reached the water. Here they encountered bad luck, a strong wind sprang up, whipping up a nasty sea, which pounded her to such an extent that it buckled her plates and frames. Had the heavy weather continued they would probably have lost her, but fortunately the weather improved quickly and the next time towage was resumed she came off though with a rather nasty list. She was towed to safety, ballasted and put on even keel, then towed to a dock, repaired and eventually sold for a good figure." With the illustration of Dorothea and tug Lyons, shown above.

Report in the Southern Times, 12.02.1916. "Abbotsbury. End of the Dorothea. The s.s. Dorothea, which, it will be recollected, was stranded and lay on the Chesil Beach a little distance from here for so long two years ago, and which was eventually re-floated, has had an eventful career. After being thoroughly repaired she was sold to a firm to be used in the London Newcastle trade, and while on a voyage in the North Sea struck a mine and sank. The crew were saved."

Go back to top

Another Iron Ore Shipwreck

In 1937 another ship that was carrying iron ore past this region was wrecked. That incident, however, was off the Isle of Wight. The 5,000 ton Italian steamer Luigi Accame was carrying iron ore from Algeria, and like the Dorothea, was also bound for Rotterdam (Medland, 1995). On April 6th, 1937, her siren was heard wailing in thick fog close to Rocken End. The coastguards fired warning rockets but to no avail. The Italian steamer ploughed onto the rocks three quarters of a mile west of St. Catherine's Lighthouse. The crew were rescued by lifeboat and eventually the ship was patched up and refloated. The bottom had been torn to shreds. It is not known whether the iron ore was magnetite and whether it is present on the sea-floor, or even on the beach here, as a consequence, but it is quite possible. The coast is shown in a photograph in Medland's book and this will give the position quite well.

Go back to top

Conclusions

Thus it seems probable that the rather unlucky ship, the S.S. Dorothea, was the source of the iron ore on the Chesil Beach near Abbotsbury. The magnetite ore seems to been covered by the beach shingle until the year 2000. It has been re-exposed by some natural removal of shingle from the front of the beach. The magnetite has a potential importance for tracing movement and behaviour patterns of pebbles on the Chesil Beach. The pebbles are easily recogisable and it could be tracked by magnetic methods. Furthermore, it is effectively coming from a point source.

Go back to top

Acknowledgements

We are very grateful to Gordon Le Pard of the Dorset Coast Forum for providing very helpful information and for copies of two of the photographs regarding the Dorothea shipwreck. His data comes from the Maritime Archaeological Record at County Hall, Dorchester, Dorset.

Go back to top

References

Please see also the reference list of the Chesil Beach - Introduction Page

.

Medland, J.C. 1995 (revised edition - previous edition 1986). Shipwrecks of the Wight. 70pp. ISBN 0 9511498 0 6. Coach House Publications Ltd., The Coach House, School Green Road, Freshwater, Isle of Wight, PO40 9BB.

Go back to top

Go to Chesil Beach -Introduction Page?

Go back to top

|Home and Contents |LWV

Copyright © 2013 Ian West, Catherine West, Tonya Loades and Joanna Bentley. All rights reserved. This is a purely academic website and images and text may not be copied for publication or for use on other webpages or for any commercial activity. A reasonable number of images and some text may be used for non-commercial academic purposes, including field trip handouts, lectures, student projects, dissertations etc, providing the source is acknowledged.

Disclaimer: Geological fieldwork involves some level of risk, which can be reduced by knowledge, experience and appropriate safety precautions. Persons undertaking field work should assess the risk, as far as possible, in accordance with weather, conditions on the day and the type of persons involved. In providing field guides on the Internet no person is advised here to undertake geological field work in any way that might involve them in unreasonable risk from cliffs, ledges, rocks, sea or other causes. Not all places need be visited and the descriptions and photographs here can be used as an alternative to visiting. Individuals and leaders should take appropriate safety precautions, and in bad conditions be prepared to cancel part or all of the field trip if necessary. Permission should be sought for entry into private land and no damage should take place. Attention should be paid to weather warnings, local warnings and danger signs. No liability for death, injury, damage to, or loss of property in connection with a field trip is accepted by providing these websites of geological information. Discussion of geological and geomorphological features, coast erosion, coastal retreat, storm surges etc are given here for academic and educational purposes only. They are not intended for assessment of risk to property or to life. No liability is accepted if this website is used beyond its academic purposes in attempting to determine measures of risk to life or property.

Go back to top

Dr Ian West, author of these webpages

Webpage - written and produced by:


Ian West, M.Sc. Ph.D. F.G.S.

.

at his private address at Romsey, Hampshire, kindly supported by the School of Ocean and Earth Science, Southampton, Southampton University and web-hosted by courtesy of the iSolutions of Southampton University. Field activities shown in this website are not necessarily those of Southampton University, some are of private visits, or of various organisations. The procedures and the safety aspects vary according to weather conditions, cliff state and whether the field trip is an organised one, a tourist trip, or merely a private visit.


.