Geol. 198B Homework #4: Optical Properties of Gems 20 pts. **

The answers to the following questions will be found in the text reading assignment, and the assigned web essays for Lesson 4.

Required Format: A 2 point penalty will be deducted for not following the format described (even if all the answers are correct)!

Send the answers to me, as an email through WebCT. Use "Homework #4" as the subject line.

As the body of the email, the answers should be arranged vertically, single file, like so:

1. b

2. quartz

3. False

4. etc....

All required answers for Homework #4 are: a multiple choice letter, True/False, or one, or two, words.

When the time period for homework submission has passed, grades will be posted which you may then view using the "My Grades" function of WebCT through the course home page.


1. A flattened disk-like cyrstal habit seen in pyrite is sometimes referred to as a(n):

a. octahedron

b. dendrite

c. puck

d. sun

e. platter

2. How many gems does the Hall text say are "always black"?


3. True or False. Gems of the tetragonal crystal system may be either dichroic or trichroic.


4. A marquis cut Andalusite will show _________ color areas, a round cut will have the colors ___________.

a. blended or mosaic-like, separate

b. trichoic, dichroic

c. dichroic, trichroic

d. color change, pleochroism

e. separated, blended or mosaic-like

5. The most recent important mine source for ruby is:


6. Which mineral is named for the fact that it will emit sparks when struck with a metal hammer?


7. A large fine quality ________ is rarer and usually more expensive than a large diamond of comparable quality.

a. pyrite

b. ruby

c. blue sapphire

d. peridot

e. Andalusite

8. High birefringence in this idiochromatic gem necessitates careful orientation to prevent a fuzzy look caused by facet doubling.

a. peridot

b. ruby

c. pyrite

d. Andalusite

e. none of the above

9. The most common inclusion found in Andalusite is:

a. carbon particles

b. rutile

c. crystals of quartz

d. growth tubes

e. bubbles

10. Rubies from Africa and _________ generally have relatively large amounts of _________as an impurity, which dampens their potential fluorescence.

______________, _____________


** "A Word to the Wise": In order to get the full 20 points on this, and every other homework, you must have all the correct answers, they must be in proper format as described above AND your email to me must be received and logged in by WebCT before the closing time for the assignment. As there are inevitable computer downtimes, disconnects and other such issues, I suggest that you do not wait until the very last moment to attempt to submit the work.