The sixteenth century Alderney crystal: a calcite as an efficient reference optical compass?
The crystal recently discovered in the 1592 sunken Elizabethan ship is shown to be an Iceland spar. We report that two main phenomena, with opposite effects, explain the good conservation and the evolution of this relatively fragile calcite crystal. We demonstrate that the Ca 2+ –Mg 2+ ion exchanges...
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crroyalsociety:10.1098/rspa.2012.0651 2024-06-02T08:09:20+00:00 The sixteenth century Alderney crystal: a calcite as an efficient reference optical compass? Le Floch, Albert Ropars, Guy Lucas, Jacques Wright, Steve Davenport, Trevor Corfield, Michael Harrisson, Michael 2013 http://dx.doi.org/10.1098/rspa.2012.0651 https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.2012.0651 https://royalsocietypublishing.org/doi/full-xml/10.1098/rspa.2012.0651 en eng The Royal Society https://royalsociety.org/journals/ethics-policies/data-sharing-mining/ Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences volume 469, issue 2153, page 20120651 ISSN 1364-5021 1471-2946 journal-article 2013 crroyalsociety https://doi.org/10.1098/rspa.2012.0651 2024-05-07T14:16:23Z The crystal recently discovered in the 1592 sunken Elizabethan ship is shown to be an Iceland spar. We report that two main phenomena, with opposite effects, explain the good conservation and the evolution of this relatively fragile calcite crystal. We demonstrate that the Ca 2+ –Mg 2+ ion exchanges in such a crystal immersed in sea water play a crucial role by limiting the solubility, strengthening the mechanical properties of the calcite, while the sand abrasion alters the crystal by inducing roughness of its surface. Although both phenomena have reduced the transparency of the Alderney calcite crystal, we demonstrate that Alderney-like crystals could really have been used as an accurate optical sun compass as an aid to ancient navigation, when the Sun was hidden by clouds or below the horizon. To avoid the possibility of large magnetic errors, not understood before 1600, an optical compass could have helped in providing the sailors with an absolute reference. An Alderney-like crystal permits the observer to follow the azimuth of the Sun, far below the horizon, with an accuracy as great as ±1 ° . The evolution of the Alderney crystal lends hope for identifying other calcite crystals in Viking shipwrecks, burials or settlements. Article in Journal/Newspaper Iceland The Royal Society Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 469 2153 20120651 |
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Open Polar |
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The Royal Society |
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crroyalsociety |
language |
English |
description |
The crystal recently discovered in the 1592 sunken Elizabethan ship is shown to be an Iceland spar. We report that two main phenomena, with opposite effects, explain the good conservation and the evolution of this relatively fragile calcite crystal. We demonstrate that the Ca 2+ –Mg 2+ ion exchanges in such a crystal immersed in sea water play a crucial role by limiting the solubility, strengthening the mechanical properties of the calcite, while the sand abrasion alters the crystal by inducing roughness of its surface. Although both phenomena have reduced the transparency of the Alderney calcite crystal, we demonstrate that Alderney-like crystals could really have been used as an accurate optical sun compass as an aid to ancient navigation, when the Sun was hidden by clouds or below the horizon. To avoid the possibility of large magnetic errors, not understood before 1600, an optical compass could have helped in providing the sailors with an absolute reference. An Alderney-like crystal permits the observer to follow the azimuth of the Sun, far below the horizon, with an accuracy as great as ±1 ° . The evolution of the Alderney crystal lends hope for identifying other calcite crystals in Viking shipwrecks, burials or settlements. |
format |
Article in Journal/Newspaper |
author |
Le Floch, Albert Ropars, Guy Lucas, Jacques Wright, Steve Davenport, Trevor Corfield, Michael Harrisson, Michael |
spellingShingle |
Le Floch, Albert Ropars, Guy Lucas, Jacques Wright, Steve Davenport, Trevor Corfield, Michael Harrisson, Michael The sixteenth century Alderney crystal: a calcite as an efficient reference optical compass? |
author_facet |
Le Floch, Albert Ropars, Guy Lucas, Jacques Wright, Steve Davenport, Trevor Corfield, Michael Harrisson, Michael |
author_sort |
Le Floch, Albert |
title |
The sixteenth century Alderney crystal: a calcite as an efficient reference optical compass? |
title_short |
The sixteenth century Alderney crystal: a calcite as an efficient reference optical compass? |
title_full |
The sixteenth century Alderney crystal: a calcite as an efficient reference optical compass? |
title_fullStr |
The sixteenth century Alderney crystal: a calcite as an efficient reference optical compass? |
title_full_unstemmed |
The sixteenth century Alderney crystal: a calcite as an efficient reference optical compass? |
title_sort |
sixteenth century alderney crystal: a calcite as an efficient reference optical compass? |
publisher |
The Royal Society |
publishDate |
2013 |
url |
http://dx.doi.org/10.1098/rspa.2012.0651 https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.2012.0651 https://royalsocietypublishing.org/doi/full-xml/10.1098/rspa.2012.0651 |
genre |
Iceland |
genre_facet |
Iceland |
op_source |
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences volume 469, issue 2153, page 20120651 ISSN 1364-5021 1471-2946 |
op_rights |
https://royalsociety.org/journals/ethics-policies/data-sharing-mining/ |
op_doi |
https://doi.org/10.1098/rspa.2012.0651 |
container_title |
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences |
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469 |
container_issue |
2153 |
container_start_page |
20120651 |
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1800755021743128576 |