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Expected Responses:
- Students should quickly realize, especially if they have had
an introduction to rocks, that they have been given representatives
of the three rock groups.
- They should be able to characterize the sedimentary rocks through
textural characteristics, although some confusion may result if they have
been given sediments (metamorphics) which may be very fine grained and even
textured. But they may show characteristics such as cleavage, or be
somewhat harder to break, etc.
- Odour. The students should be given specimens which have an odour.
Darker rocks, and in particular limestones which are dark grey in colour,
are the best. If they have had the advantage of testing the "muck", there
may be some rich organic smells. It is important to note that the odours
are produced by the often unseen contents of the rocks. They may in fact
be sulphurous in smell due to hydrogen sulphide. Sulphur may be in
mineral form, but the gas will tip you off that there was production
of this compound through reducing conditions which are common to poorly
oxygenated water.
Many freshly broken rocks will have some smell but the conclusions
reached should indicate that only the sedimentary rocks have the "organic"
smell, and among those only the darker coloured ones.
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