ROCK AND MINERAL REVIEW:
Learning Objectives
In historical geology rocks are used as tools to decipher the past. The rocks become important
because of the clues they give to the Earth’s history.
Some review terms:
Quartz*: hard glassy mineral that often remains unchanged during weathering.
Feldspar*: a common rock forming mineral that weathers to form clay
Ferromagnesium minerals (ferromags)*: common rock forming minerals, rich in iron
and magnesium, weathers to form clay
Carbonates*: group of rocks that all contain calcium carbonate
Evaporites: group of minerals including halite* and gypsum* that form from evaporation
of water bodies
In historical geology rocks are important for the clues they contain that unlock the Earth’s
history.
Igneous Rocks:
Igneous rocks form from solidification of a melt, they are important in historical geology because
they often contain elements that can be used for radiometric dating.
The sea floor is composed of basalt and the magnetic characteristics of the sea floor helped build
the theory of plate tectonics.
Metamorphic Rocks:
Metamorphic rocks form from heat and/or pressure. They are important in historical geology
because they indicate the presence of a magma or a past orogenic event.
Sedimentary Rocks:
Sedimentary rocks form from the lithification of sediments and are the most important rocks for
deciphering the Earth’s history.
* Mineral photographs courtesy of Amythest Galleries
