Homeworks 14 and 15
Silicates I and II
Name _____________________
A. Lecture on Silicates I
Part 1 Follow along in the PowerPoint and answer the following:
1. Explain why Silicates are the most abundant minerals.
2. Calculate the charge of the SiO4 anionic complex.
3. List the silicate types in order of crystallization from hottest to coolest
from a basaltic melt.
4. Explain how Silicates polymerize.
5. Explain why silicate ion tetrahedra don’t share faces or edges.
6. Which has a stronger Al – 0 bond, (choose: Al+3 in tetrahedral
coordination / Al+3 in octahedral coordination). Hint: check Electrovalency.
7. Name the biggest and smallest ions. Be sure to show their charge.
Part 2 Match the Terms
8. Single chain Inosilicates ______
a. Olivines
9. Framework - Tectosilicates _____ b. Micas
10.Sheets - Phyllosilicates ______
c. Feldspars
11.Double Chain Inosilicates ____
d. Amphiboles
12.Independent Tetrahedra ____
e. Pyroxenes
Part 3 Continue along in the PowerPoint and answer the following:
13. What is the generalized anionic formula for a Nesosilicate?
14.Why does Olivine have two metals per silicate ionic complex,
(Mg,Fe)2SiO4 , but Zircon ZrSiO4. has only one metal per silicate ionic
complex?
15. The generalized formula for Garnets is A3B2Si3O12
The B position in Garnet is usually Aluminum ion Al+3 . The
Aluminum is (choose: in tetrahedral coordination / in octahedral
coordination).
16. Look at the phase diagram for Al2SiO5.
a. How many components?
b. How many phases?
c. Which phase has the lowest Gibbs Free Energy for
P = 5 kilobars and T = 875oC?
17.What is the hardness of Topaz?
18.Describe the appearance of Staurolite in a Muscovite Schist.
19.In Epidote, Aluminum ion Al+3 is in octahedral coordination [6] with six
oxygens OR four oxygens plus two ___________ ions.
20.The sorosilicate Hemimorphite, Zn4(Si2O7)(OH)2.H2O
most frequently occurs as the product of the oxidation of the upper
parts of Sphalerite ZnS bearing ore bodies, accompanied by other
secondary minerals which form the so-called iron cap or
___________.
B. Lecture on Silicates II
1. Tourmaline contains Boron. True or False?
2. Name three (3) Clinopyroxenes.
3. Name two (2) Orthopyroxenes. (Hint: Pigeonite is monoclinic).
4. Clinopyroxenes belong to the Orthorhombic Crystal System. True or
False?
5. There is complete Mg-Fe solid solution between Diopside and
Hedenbergite. True or False?
6. Pigeonite, a Clinopyroxene, is only stable at higher temperatures and
exsolves to Augite plus an Orthopyroxene if cooled slowly to lower
temperatures. True or False?
7. Two cleavages at about 90o are visible in pyroxenes when looking down
the (choose: a – axis / b-axis / c – axis).
8. In Amphiboles, the largest Ions (Na+ or K+ ) sit between the double
chains of silicate tetrahedra. True or False?
9. In the pyroxenoid Wollastonite, CaSiO3 , the orientation of silicate
tetrahedra repeats every (choose: third / fifth / seventh) tetrahedron.
10. Explain why all the octahedral sites in Phlogopite have magnesium ions,
but in Muscovite two of every three octahedral sites are vacant.
11. Examine the Phase Diagram for SiO2
a. How many components? _____
b. How many phases can you find? ____
c. Which phase has the highest entropy?____________
12. Consider the pyroxene Enstatite (MgSiO3). The Gibbs Free Energy of
Formation for Enstatite from pure elements (Mg, Si and O) = ΔGf
(Enstatite, elements) is about -1,460.9 Joules*/mole at room temperature
and pressure.
Since the ΔGf values for Enstatite is negative, this means that
Enstatite is more stable than, and will form from, the separate
elements.
a. True
b. False
* BTW: a Joule is a unit of energy, it has units Watts x seconds
http://www.kean.edu/~csmart/Mineralogy/Lectures/Gibbs%20Free%20Energy%20of%20Formation.pdf