- Email: [email protected]
Ant hill mob
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THE LAST WORD Mystery lith This very heavy, non-magnetic boulder was unearthed from swampy land near limestone caves in northern New Zealand (see below). What is it?
from as small as a centimetre to several metres in diameter. Even the iron carbonate in concretions is not ferromagnetic, so all forms of these objects would appear non-magnetic if a magnet were held to them. Michael Pearson Crieff, Perthshire, UK
n It is most likely to be a concretion – a hard, solid mass of matter formed in a softish rock such as mudstone by the n I have seen this boulder outside near-spherical growth of a harder the caves at Waiomio, north of the mineral cement. This material is city of Whangarei. It appears to be usually a carbonate of calcium, a concretion, probably weathered magnesium, manganese or iron out of the rocks of the Northland that collected during shallow Allochthon. These rocks overlie burial of the sediment before the Oligocene limestone in which it became fully lithified. the caves occur but have been These objects are quite removed locally by erosion. common in some of the Such concretions are common mangrove areas of Northland, in parts of Northland. Some wellNew Zealand, where repeated “The cave proprietors were washing by a tidal water flow claiming the boulder was a has removed the soft mudstone. meteorite, probably misled They are also found in soils away by its high density” from the coast, so this one could have come from a mudstone or shale underlying the limestone known examples are on display where the caves formed. near the Stanley Street entrance to No scale is given in the picture, the Auckland Domain park, where but such concretions can range they were relocated from their original location in the Auckland suburb of Silverdale. The heaviness of these concretions is caused by the dense mineral baryte (barium sulphate), a common mineral in concretions. The formation mechanism is the same as that for the much more famous Moeraki Boulders on New Zealand’s South Island. A nucleus (usually a fossil) causes precipitation of cementing minerals from water percolating through a permeable sedimentary
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.
rock. If the sediment is reasonably homogeneous, the zone of cementation will grow equally in all directions, producing a solid sphere of rock. The cemented volume is more resistant to erosion than the surrounding strata and can eventually be left behind as an isolated spherical boulder when the rest is removed. When I last visited the caves where the photo was taken, the proprietors were claiming the boulder was a meteorite, probably misled by the rock’s high density. Paul Keestra Auckland, New Zealand
pristine sand dune. One of them seems to be a trail left in the surface by a passing arthropod. The other has a mound-like relief and it appears to have been made by the sand being pushed upwards from below. The mounds’ height and width are generally uniform along their length, at perhaps 1 and 1.5 centimetres, respectively; there are branches at several points; and nowhere do there seem to be openings to the surface. Does anyone have an explanation? Howard Ritter Fuquay-Varina, North Carolina, US
This week’s questions
While mowing the grass, I noticed that in several places ant nests were situated under clumps of daisies. Do the ants choose to nest under daisies, or do these flowers grow where they do because of the ants’ activity? Peter Waller Bristol, UK
Underground LINE
On a March visit to the North Carolina seashore, I encountered this tableau (above) of two types of markings on an otherwise
ant hill mob
Question Everything The latest book of science questions: unpredictable and entertaining. Expect the unexpected Available from booksellers and at newscientist.com/questioneverything
THE LAST WORD Mystery lith This very heavy, non-magnetic boulder was unearthed from swampy land near limestone caves in northern New Zealand (see below). What is it?
from as small as a centimetre to several metres in diameter. Even the iron carbonate in concretions is not ferromagnetic, so all forms of these objects would appear non-magnetic if a magnet were held to them. Michael Pearson Crieff, Perthshire, UK
n It is most likely to be a concretion – a hard, solid mass of matter formed in a softish rock such as mudstone by the n I have seen this boulder outside near-spherical growth of a harder the caves at Waiomio, north of the mineral cement. This material is city of Whangarei. It appears to be usually a carbonate of calcium, a concretion, probably weathered magnesium, manganese or iron out of the rocks of the Northland that collected during shallow Allochthon. These rocks overlie burial of the sediment before the Oligocene limestone in which it became fully lithified. the caves occur but have been These objects are quite removed locally by erosion. common in some of the Such concretions are common mangrove areas of Northland, in parts of Northland. Some wellNew Zealand, where repeated “The cave proprietors were washing by a tidal water flow claiming the boulder was a has removed the soft mudstone. meteorite, probably misled They are also found in soils away by its high density” from the coast, so this one could have come from a mudstone or shale underlying the limestone known examples are on display where the caves formed. near the Stanley Street entrance to No scale is given in the picture, the Auckland Domain park, where but such concretions can range they were relocated from their original location in the Auckland suburb of Silverdale. The heaviness of these concretions is caused by the dense mineral baryte (barium sulphate), a common mineral in concretions. The formation mechanism is the same as that for the much more famous Moeraki Boulders on New Zealand’s South Island. A nucleus (usually a fossil) causes precipitation of cementing minerals from water percolating through a permeable sedimentary
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.
rock. If the sediment is reasonably homogeneous, the zone of cementation will grow equally in all directions, producing a solid sphere of rock. The cemented volume is more resistant to erosion than the surrounding strata and can eventually be left behind as an isolated spherical boulder when the rest is removed. When I last visited the caves where the photo was taken, the proprietors were claiming the boulder was a meteorite, probably misled by the rock’s high density. Paul Keestra Auckland, New Zealand
pristine sand dune. One of them seems to be a trail left in the surface by a passing arthropod. The other has a mound-like relief and it appears to have been made by the sand being pushed upwards from below. The mounds’ height and width are generally uniform along their length, at perhaps 1 and 1.5 centimetres, respectively; there are branches at several points; and nowhere do there seem to be openings to the surface. Does anyone have an explanation? Howard Ritter Fuquay-Varina, North Carolina, US
This week’s questions
While mowing the grass, I noticed that in several places ant nests were situated under clumps of daisies. Do the ants choose to nest under daisies, or do these flowers grow where they do because of the ants’ activity? Peter Waller Bristol, UK
Underground LINE
On a March visit to the North Carolina seashore, I encountered this tableau (above) of two types of markings on an otherwise
ant hill mob
Question Everything The latest book of science questions: unpredictable and entertaining. Expect the unexpected Available from booksellers and at newscientist.com/questioneverything