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GEOL 211 Mineralogy
October 3, 2000
First Midterm Exam

(15) 1. Give concise definitions for the following terms:

a. Mineral -

b. Eight most abundant elements in the crust are (list) -

c. Solid solution -

d. Open form -

e. Twinning -

(20) 2. a. What three environmental parameters (conditions) define the conditions under which a specific type of mineral or mineral assemblage will form in a rock during crystallization or recrystallization?

b. What quantity is always minimized when a geochemical system (i.e. mineral, rock, magma, water solution, etc.) undergoes a spontaneous change in state (i.e. crystallizes, dissolves, recrystallizes, melts, etc.).

c. Briefly compare and contrast metastable and stable states for a system.

d. When holding a piece of granite in your hand (i.e. a phaneritic assemblage of feldspars, quartz and micas), would the minerals be considered to be in a stable or a metastable state? Briefly explain you reasoning.

(15) 3. Evaluate the following stuctural formula:

(Ca, Na)(Mg, Fe2+, Al)(Si, Al)2O6

Three crystallographic sites are indicated (tetrahedral, cubic and octahedral).

a. Which of the indicated three types of sites contains Si and Al?

b. What is the coordination number for the site containing Ca and Na?

c. What is the geometry of the name of the coordination polyhedra for the site containing Mg, Fe2+, and Al?

d. List an element which might be expected to substitute for Ca, and briefly explain your reasoning.

e. Based on the structural formula, what type of silicate is this? (i.e. nesosilicate, sorosilicate, etc.) Briefly explain your reasoning.

(20) 4. A mineral has the following crystallographic properties: Tormey


Axial ratios = 1:2:4

Forms: {011}, {001}and {110}

a. Name the crystal system: (HINT: one two-fold axis perpendicular to a mirror plane)

b. Name the three forms:

c. Make a sketch showing how the mineral would look if view down the a-axis.

d. Make a sketch showing how the mineral would look if view down the c-axis.

(15) 5. a. Describe the fundamental symmetry characteristics that distinguish tetragonal from isometric minerals.

b. Describe the fundamental difference between nesosilicates and sorosilicates (make a sketch to help illustrate the difference).

c. Of the seven silicate groups described in class, which would you expect to occur in rocks with highest Si to O ratios (i.e. highest content of SiO2). Briefly explain your reasoning.

(10) 6. (a) Briefly describe the two types of defect structures commonly found in minerals.

b. Briefly explain the significance of defect structures in minerals.

(5) 7. (a) The most common mineral in the crust is:

b. The most common mineral in the upper mantle is:

EXTRA (2 points) The most common mineral in the entire earth is:

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