A Rock Cycle Chart
This chart of the Rock Cycle is available from a number of vendors, for
teaching about rock types and the interconversion among rock types. This
is a high-quality plastic chart that contains niches into which actual
samples of rock can be placed. As stated by the developers of this study
aid, a number of features have been oversimplified, in order to illustrate a
number of different concepts on a single chart. The preceding “short
lesson” was developed to help teachers at a workshop see where the
oversimplifications might be. Several are:
- Currently-forming sediment is shown dipping beneath the mountain
range and cementing into rock. This is a fusion of several concepts:
tectonic plate subduction (dipping of the sediment), cementing of sediment
into rock when the sediment has been buried deeply enough, and the
horizontal layering of sediment as it accumulates in lake and sea bottoms.
In nature, these three processes do not occur as illustrated here.
- Magma intrusions typically cause uplift of overlying strata. While there
are many examples of magma extruding through cracks and fissures in
overlying strata (as shown here), we more commonly find strata on the
flanks of magma intrusions tilting upward in response to uplift by the
magma chamber. It is not usually the case that the strata on the flanks of
the magma intrusion dip downward.