Minerals as indicators of the environment of their formation

By: Brian J. Skinner e Stephen C. Porter, The Dynamic Earth an introduction to physical geography, Wiley, 1992

Read the text and answer the questions

Minerals should not be regarded merely as objects of beauty or sources of economically valuable materials. Contained within their makeup are the keys to the conditions under which they (and the rocks they are in) formed. The study of minerals, therefore, can provide insight into the chemical and physical conditions in regions of the Earth we cannot observe and measure directly.
Our understanding of the growth environments of minerals has come largely through studying minerals in the laboratory. By suitable experiments, for example, scientists have been able to define the temperatures and pressures at which a diamond will form rather than its polymorph, graphite. Because we can infer how temperature and pressure increase with depth in the Earth, we can state with certainty that rocks in which diamonds are found are samples of the mantle from at least 150 km below the Earth’s surface. Another example concerns weathering. The minerals that form in the regolith during weathering are controlled by the climate cold and wet versus hot and dry, for example. Past climates can therefore be deciphered from the kinds of minerals preserved in sedimentary rocks. The composition of seawater in past ages can also be determined from the minerals formed when seawater evaporated and deposited its salts.

1. Which is the formation environment of a feldspar bearing rock?
2. What are the differences between the formation environments of diamond and graphite?
3. What helped scientists to understand the growth environments of minerals?
4. What does a bauxite tell about its formation environment? What is a gypsum bearing rock?

Test your knowledge

1. Write the term that best completes each sentence.
   1. Compound minerals made up of oxygen and silicon are called.....................
   2. A regular, geometric solid with smooth surfaces is called a...........................
   3. Atoms of the same element having different numbers of neutrons are called...........................
2. What is the Mohs Scale?
3. Complete the concept map.