2. The octet rule states that atoms bond with other atoms in such a way as to have their outer shell full of electrons. Generally an atom’s outer shell is full when it has 8 electrons in it.
The number of valence electrons that an atom has determines how it will bond to other atoms.
3. In ionic bonding a mutual give and take of electrons occurs between the atoms that are bonding, which causes the atoms to take on opposite charges and therefore mutually attract. In covalent bonding one or more valence electrons are shared between atoms.
4. Most mineral samples do not demonstrate their crystal form because they get crowded against other crystals.
5. The single tetrahedron silicate structure requires the addition of the greatest number of positive ions (metals) to achieve electrical neutrality.
6. In feldspar, Al substitutes for Si in about 25% of the tetrahedra. Al (+3) is not as positive as Si (+4) so metal ions like Ca+2, Na+1, and K+1 are needed to make-up the difference.
7. All ferromagnesian minerals contain Fe and/or Mg. They also contain silica.
Four examples of ferromagnesian minerals:
Olivine - it’s isolated silicate structure implies a high concentration of Fe and Mg but little silica.
Augite - it’s single chain silicate structure implies a bit more silica than olivine, but less Fe and Mg. Augite is the most common mineral in the pyroxene group.
Hornblende - a double chain silicate, it is the most common amphibole.
Biotite - a sheet silicate and a mica, it contains more silica and less Fe and Mg than all of the above ferromagnesians.
8. Muscovite and biotite are both micas. They differ in that biotite is a ferromagnesian silicate, whereas muscovite is a non-ferromagnesian silicate.
9. Orthoclase and plagioclase are both feldspars and thus both contain Al as well as silica. They differ in that orthoclase contains K, whereas plagioclase contains Ca and/or Na.
10. a. hornblende
b. muscovite
c. quartz
d. olivine
e. plagioclase
f. clay
11. The same mineral can have different colors, and different minerals have the can have the same color.
12. If a sample contains calcite it will effervesce (fizz) on contact with HCl (hydrochloric acid).
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This page was updated on 08/18/2014 08:31 PM
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