Electron Optics Image Gallery 3

Here is my personal selection of images of some of the samples that have passed through our SEM laboratory in the past few months. As usual, I have endowed a number of them with false colour. All images were taken on the CamScan Series 4 SEM, unless otherwise indicated.

Click on the thumbnails to see the full image.

Helena Eklund is working with Jane Francis on the flora of Table Nunatak, just east of Kenyon Peninsula on the eastern side of the Antarctic Peninsula. Shown here is an example of a charcoalified angiosperm seed with a reticulate seed coat composed of strongly pitted cells. It is from the late Santonian (Upper Cretaceous, ca 80 million years ago).

A number of complete but desiccated, juvenile echinoderms (probably 'regular' Euechinoidea) have been sitting in my desk draw for some time. Here is a view of one mounted upside down (peristome uppermost). The teeth of the Aristotle's Lantern (mouth and jaw) can be seen protruding through the peristomal membrane, with the spines visible in the background. Unfortunately the desiccation process has left a large number of sand grains stuck to the test, hiding detail of the attachment of the spines.

View of a fragment of the test of a defleshed example of the previous echinoid. A column of ambulacral plates is on the left, interambulacral plates are on the right. Note the double line of pores for the tube feet and the prominent spine bosses.

Bruce Yardley and Dave Banks have been testing the suitability of different lasers for the fluid inclusion work planned for the new laser ablation ICP-MS. Here is a test laser ablation pit in an emerald from Afghanistan produced by a 193nm Ultra Violet Excimer laser.

One of Liane Benning's research projects concerns the nucleation and growth of colloidal iron sulphides. Here is an image of colloidal greigite (magnetic iron sulphide - FeFe₂S₄) that I took on the new FEG SEM in the Department of Materials.

M.Sc. Geochemistry Projects 2000 - 2001.

As in the last gallery of images, here are some of the SEM micrographs taken from the M.Sc. Geochemistry projects.

Kathryn Manser studied modern hot spring biomineralisation. This image shows biosilicification of prokaryotic bacteria. For more information contact Kurt Konhauser or Liane Benning.

David Worton devised a laboratory simulation of a venting hydrothermal system, and attempted the in situ pyritisation of modern cockle shells. This was partially successful, but what was much more fun was the growth of gypsum crystals on the cockle shells as they dried out on removal from the reacting solution.
For more information contact Liane Benning.

Robert Wilson studied the retrograde dolomitisation of the Loch Tay Limestone, SW Scotland, as revealed by the variation in d¹⁸O values. This BSE image of a zoned dolomite shows an electron microprobe traverse, outlined in red, with analysis spots at 2 µm intervals. The data from this traverse was used to correct the d¹⁸O values from the ion probe traverse - the larger triangular pits. For more information contact Andrew McCaig.

The First Year Teaching Collection

It recently occurred to me that it might be worth examining, on the SEM and microprobe, an example of each of the fifty or so rock types that comprise the 1st year teaching collection - just to see if we have been missing anything all these years. Here is a preliminary look at three of the sedimentary rocks that the first years examined in weeks 8 and 9. BSE, 'probe data and CL images will be added once polished material is available.

Rock 21. Red aeolian sandstone. Triassic. Penrith, Cumbria, U.K.

A pure sandstone (feldspar is present, but rare). The characteristic feature of this rock is that each of the well rounded clasts has an overgrowth of diagenetic quartz that in many instances has been able to grow unhindered into pore spaces. Images 21a, 21b and 21c show details of this relationship.

a.b.c.

Rock 27. Oolitic limestone. Upper Jurassic. Pickering, North Yorkshire, U.K.

This is one of those situations where an eyeball and hand lens are probably better optical equipment for getting an overview of the specimen than the SEM, primarily because the fine grained nature of the carbonate making up the ooliths scatters the electrons so badly that the surface appears 'noisy' (image 27a). However what is not easily appreciated under the hand lens is the nature of the relationship between the ooliths and the coarser calcite cement. This is well picked out in images 27a and 27b. Image 27c shows the interlocking carbonate rhombs that constitute the ooliths.

a.b.c.

Diatomaceous (?) Earth (Diatomite). Age and provenance unknown.

This sample is part of the sedimentary rocks demonstration set. Unfortunately it has no acquisition number, and nobody seems to know where it came from or its age. One would have thought that biologics extracted from a diatomaceous earth would have been diatoms. But no. Dr. Jean-Henri Hecq of the Laboratory of Plankton Ecohydrodynamics, University of Liege, Belgium has pointed out that these images are probably of protozoan radiolaria. So our diatomaceous earth is probably a radiolarian earth instead. Image a shows the general nature of the sample. Most of the radiolaria are crushed, but with a bit of care some reasonably whole examples can be separated out. A selection of the types found are shown in images b, c, and d.

a.

b.c.d.

Eric Condliffe
January 2002

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