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Duck stone
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THE LAST WORD Duck stone I found a grey stone with an image of a white bird on a beach in north Donegal, Ireland. How would this structure have been formed? How did the white rock get into the grey rock?
n The “duck stone” is an excellent find. Knowing it comes from Donegal doesn’t help much with identification of the rock type, but it looks like a fine-grained, homogeneous rock that has been broken by a series of small-scale earth movements producing cracks with different, intersecting alignments. Further ground movements n The white rock is probably a common mineral, quartz, and widened the cracks and created the grey around it is probably a space that has been filled limestone, although it could be by mineral solutions seeping clay, mudstone, sandstone or through the rock and depositing siltstone – the grain size can’t be pale-coloured crystalline material seen clearly, so it is hard to say. such as quartz or calcite. At the It is most likely that this rock time, this rock would have been was weathered in the sea or a deep underground where river, as it has fairly smooth pressures are high, so the surfaces. Over time, this would cementing of the rock types reveal more of the quartz, but it has been almost perfect. Glaciers covered this area later on, when the rock was nearer the “You see a white bird in a rock on a beach – is this surface. As the glaciers moved, like an inkblot test for they broke off a chunk of rock geologists?” that was the precursor to this pebble. Its movement by ice and is sheer chance that it looks like a water has since given it a more duck right now, controlled by the rounded form. shape of the spaces in the rock The circular patterns we can that the quartz filled in. now see are caused by the It is worth noting that the host intersection of the crack features rock might be softer than the on the curved surface of the quartz. Eventually that “image”, cobble as it is today. if the stone is allowed to weather Jonathan Wilkins further, may well reveal a Haulfryn, Conwy, UK
We pay £25 for every answer published in New Scientist. To answer a question or ask a new one please email [email protected]. Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address. You can also send questions and
answers to The Last Word, New Scientist, 25 Bedford Street, London, WC2E 9ES. New Scientist Ltd retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format and at any time in the future. All unanswered questions and previous questions and answers are at newscientist.com/lastword/
different shape, and, before that happens, the quartz will stand out from the rock around it. Limestone, in particular, is susceptible to weathering by rainwater, which is a weak solution of carbonic acid. Massively scaled up, this is how caves form. Other rock types are harder and take longer to weather. Helen Gould Peterborough, Cambridgeshire, UK n The pebble could be granite, a rock type typical of coastal Donegal, veined with quartz. Veins, which have branching sheet-like appearances, form when minerals carried in an aqueous solution within the rock are precipitated in cracks and voids. Gerald Legg Hurstpierpoint, West Sussex, UK n Your grey pebble is probably a siltstone about 1 billion years old, which was metamorphosed – changed and warped by heat or pressure – about 700 million years ago. When this happened, it distorted cracks in the rock filled with veins of milky quartz. Tumbling of this pebble on the beach has sculpted it into an intriguing shape, but basically there were two planes of intersecting quartz veins. Any resemblance to a duck is purely coincidental – an example of pareidolia, which is the tendency to see faces or animals in inanimate objects. Geoff Townson Charmouth, Dorset, UK
Watch 100 fascinating science talks! Watch mind-expanding talks from Anne-Marie Imafidon, Carlo Rovelli, Tim Peake, Megan Rossi, and many other inspiring scientists. Visit newscientist.com/nsltalks
n I have seen many similar stones, ranging from pebbles to boulders, in the Whanganui river valley in New Zealand. This river runs through rock that started out as sediment deposited at the bottom of a shallow sea. The white parts of the stone mark spots where shells were buried in the sediment, revealed in cross-section on the water-worn surfaces. The most common are bivalves similar to oysters, which often appear as arcs or ellipses, but conical shells are also common. Tony Ellis Titahi Bay, New Zealand n They see a white bird in a rock on a beach in Donegal... is this like an inkblot test for geologists? Holland Oates, Cleveland, Ohio, US
This week’s questions INTIMATE CONTACT
From a pathogenic perspective, which is more dangerous, to be licked by an animal or kissed by a human? Al Cowie Oxford, UK BEE TOUGHER
Almost every pest organism, from weeds to rats, seems able to develop resistance to chemicals used to kill them. Yet honeybees seem unable to resist the chemicals said to be contributing to their decline. Why? Joe Majewski Rindge, New Hampshire, US
THE LAST WORD Duck stone I found a grey stone with an image of a white bird on a beach in north Donegal, Ireland. How would this structure have been formed? How did the white rock get into the grey rock?
n The “duck stone” is an excellent find. Knowing it comes from Donegal doesn’t help much with identification of the rock type, but it looks like a fine-grained, homogeneous rock that has been broken by a series of small-scale earth movements producing cracks with different, intersecting alignments. Further ground movements n The white rock is probably a common mineral, quartz, and widened the cracks and created the grey around it is probably a space that has been filled limestone, although it could be by mineral solutions seeping clay, mudstone, sandstone or through the rock and depositing siltstone – the grain size can’t be pale-coloured crystalline material seen clearly, so it is hard to say. such as quartz or calcite. At the It is most likely that this rock time, this rock would have been was weathered in the sea or a deep underground where river, as it has fairly smooth pressures are high, so the surfaces. Over time, this would cementing of the rock types reveal more of the quartz, but it has been almost perfect. Glaciers covered this area later on, when the rock was nearer the “You see a white bird in a rock on a beach – is this surface. As the glaciers moved, like an inkblot test for they broke off a chunk of rock geologists?” that was the precursor to this pebble. Its movement by ice and is sheer chance that it looks like a water has since given it a more duck right now, controlled by the rounded form. shape of the spaces in the rock The circular patterns we can that the quartz filled in. now see are caused by the It is worth noting that the host intersection of the crack features rock might be softer than the on the curved surface of the quartz. Eventually that “image”, cobble as it is today. if the stone is allowed to weather Jonathan Wilkins further, may well reveal a Haulfryn, Conwy, UK
We pay £25 for every answer published in New Scientist. To answer a question or ask a new one please email [email protected]. Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address. You can also send questions and
answers to The Last Word, New Scientist, 25 Bedford Street, London, WC2E 9ES. New Scientist Ltd retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format and at any time in the future. All unanswered questions and previous questions and answers are at newscientist.com/lastword/
different shape, and, before that happens, the quartz will stand out from the rock around it. Limestone, in particular, is susceptible to weathering by rainwater, which is a weak solution of carbonic acid. Massively scaled up, this is how caves form. Other rock types are harder and take longer to weather. Helen Gould Peterborough, Cambridgeshire, UK n The pebble could be granite, a rock type typical of coastal Donegal, veined with quartz. Veins, which have branching sheet-like appearances, form when minerals carried in an aqueous solution within the rock are precipitated in cracks and voids. Gerald Legg Hurstpierpoint, West Sussex, UK n Your grey pebble is probably a siltstone about 1 billion years old, which was metamorphosed – changed and warped by heat or pressure – about 700 million years ago. When this happened, it distorted cracks in the rock filled with veins of milky quartz. Tumbling of this pebble on the beach has sculpted it into an intriguing shape, but basically there were two planes of intersecting quartz veins. Any resemblance to a duck is purely coincidental – an example of pareidolia, which is the tendency to see faces or animals in inanimate objects. Geoff Townson Charmouth, Dorset, UK
Watch 100 fascinating science talks! Watch mind-expanding talks from Anne-Marie Imafidon, Carlo Rovelli, Tim Peake, Megan Rossi, and many other inspiring scientists. Visit newscientist.com/nsltalks
n I have seen many similar stones, ranging from pebbles to boulders, in the Whanganui river valley in New Zealand. This river runs through rock that started out as sediment deposited at the bottom of a shallow sea. The white parts of the stone mark spots where shells were buried in the sediment, revealed in cross-section on the water-worn surfaces. The most common are bivalves similar to oysters, which often appear as arcs or ellipses, but conical shells are also common. Tony Ellis Titahi Bay, New Zealand n They see a white bird in a rock on a beach in Donegal... is this like an inkblot test for geologists? Holland Oates, Cleveland, Ohio, US
This week’s questions INTIMATE CONTACT
From a pathogenic perspective, which is more dangerous, to be licked by an animal or kissed by a human? Al Cowie Oxford, UK BEE TOUGHER
Almost every pest organism, from weeds to rats, seems able to develop resistance to chemicals used to kill them. Yet honeybees seem unable to resist the chemicals said to be contributing to their decline. Why? Joe Majewski Rindge, New Hampshire, US