Geol. 198B Homework #6: Optical Phenomena in Gemstones 20 pts. **

The answers to the following questions will be found in the text reading assignments, and the assigned web essays for Lesson 6.

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 #6" 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 #6 are: a multiple choice letter, True/False, or one word.

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. Which of the species below is most likely to show the optical phenomenon of aventurescence?

a. corundum

b. moonstone

c. lepidolite

d. opal

e. asteria

2. Most star corundums are of a light blue or grey color and come from the country of:


3. Tiger iron is a rock composed primarily of tiger'seye and:

a. hawk'seye

b. jasper

c. serefinite

d. coral

e. none of the above


4. True or False. According to Lyman, "harlequin" is the most valuable pattern of colors in a precious opal.


5. Heating of corundum, as it is commonly done to improve color and clarity, tends to (diminish/enhance) its star-making potential. (choose one)


6. A white opal simulant made of glass has been produced under the trade name:

a. Slocum stone

b. Gilson opal

c. fire opal

d. Andamooka opal

e. potch

7. A star corundum can be:

a. natural, unenhanced

b. natural, diffusion enhanced

c. synthetic

d. any of the above

e. only a or c

8. The wavelength intensity of daylight is highest at about _______nm and that of incandescent light at about ______nm.

a. 700/575

b. 450/625

c. 625/450

d. green/violet

e. 575/700

9. If a gem changes color very subtly when viewed in different light sources, it is said to be exhibiting:

a. metamerism

b. The Alexandrite Effect

c. pleochroism

d. color zoning

e. fluoresence

10. True or False. The star figure seen in specimens of trapiche emeralds or chiastolite are optical phenomena.



** "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.