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There are two separate parts to this programme; the first half relates the optical properties of minerals to symmetry and crystal shape; the second half introduces geological mapwork. Professor Ia...n Gass, Professor of Earth Sciences at the Open University introduces the two speakers, John Wright, Reader in Earth Sciences, and Dr. Chris Wilson, Senior Lecturer in Earth Sciences. A model of a crystal of quartz is used to show the position of the three-fold axis of symmetry. Other models are used to show how thin section can be cut at any angle to this axis. Thin sections of quartz crystals of known orientation are compared in a polaroid apparatus. They show the full range of possible polarisation colours in quartz, including the isotropic basal section. A similar demonstration is done for the mineral biotite. It shows the variation in optical properties according to the orientation of the section. However, in this case the properties are related to the atomic structure of bictite. The second part of the programme starts with a bird's eye view of the sort of places where rocks can be seen at the earth's surface. Helicopter shots show the gritstone edges in Derbyshire, mountains in Wales, the Pembroke Coast, the Cheddar Gorge, and a variety of man-made and temporary exposures. A model is used to show the intersection of a geological bed with hills and valleys. Stratum contours and topographic contours for the model are superimposed to explain why a simple geological structure appears to have such a complex outcrop pattern.
Metadata describing this Open University video programme
Item code: S23-; 03
First transmission date: 19-02-1972
Published: 1972
Rights Statement:
Restrictions on use:
Duration: 00:24:14
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Producer: Peter Clarke
Contributors: Ian Gass; John Wright
Publisher: BBC Open University
Keyword(s): Atomic structure; Biotite; Derbyshire; Gritstone edges; Isotropic basal section; Pembroke coast; Polarisation colours; Polaroid apparatus; Stratum contours; Three-fold axis of symmetry
Footage description: Ian Gass introduces the programme. He introduces John Wright. John Wright with a quartz crystal and with an idealised model of a quartz crystal. He examines the model's symmetry and points out its three fold axis. Wright uses a series of models to show how thin sections can be cut at any angle to this axis. He mounts actual quartz sections in a polarising microscope. As the sections are rotated they shot the full range of possible polarisation colours, Wright demonstrates that a section cut perpendicular to the axis is isotropic. John Wright with a crystal fragment of biotite. He also has a molecular model of the crystal structuire. Wright points out its layer structure and cleavage plates. Sections of biotite crystal cut at various angles are shown under the polarising microscope and rotated. John Wright sums up. Ian Gass introduces the section on geological map work and Chris Wilson. Chris Wilson with a geological map. He points out the two main features found in geological maps - outcrop pattern and topographic contours. Helicopter film shots of a scarp showing carboniferous limes tine. More aerial shots of rocks of mountains of Wales, the Pembroke coast, the Cheddar Gorge and a variety of man made temporary exposures. Commentary by Chris Wilson. Chris Wilson uses a geological model to show the intersection of a geological bed with hills and valleys. Stratum contours and topographic contours for the model are superimposed to explain why simple geological structures appear to have complex outcrop patterns. Wilson recaps with 2 dimensional representations showing stratum, topographical and superimposed contours. He explains how the outcrop can be plotted from information found on the superimposed contour map and demonstrates.
Master spool number: 6LT/70295
Production number: 00521_2152
Videofinder number: 1710
Available to public: no