Which minerals are most important? (2.7) What will be an ideal ...

[awywial]

Which minerals are most important? (2.7)
 
  What will be an ideal response?

Question 2

Briefly describe the concept behind a TEM detector. (2.4)
 
  What will be an ideal response?

[vish98]

Answer to Question 1

Answer: Minerals are most important if they are common in rocks, provide essential resources, or both. Silicate minerals are the primary rock-forming minerals in the crust. More than 4,000 minerals have been identified, but only a few dozen are important as rock-forming minerals, because only 12 of the 89 naturally occurring elements compose 99.7 percent of Earth's crust. However, most economically valuable metals are processed from nonsilicate ore minerals, especially oxide and sulfide minerals, so not only silicate minerals are important

Answer to Question 2

Answer: Most of the size of an atom consists of the cloud of electrons that orbit the nucleus. If many electrons exist in a small area around the nucleus, then there is a good chance that electrons fired in the TEM will collide with an orbiting electron and bounce off it, rather than continuing through to the detector. If, however, the electrons are widely spaced around a nucleus, then the fired electrons may pass through the atom without hitting any obstacles. This means that the shadows in the TEM image may not represent all of the types of atoms in a mineral, but rather only the atoms with closely clustered electrons.