Quiz 2 review
Good work on Quiz 2! The average on the quiz was ~16.1, and the following
questions were some of the most commonly mis-answered. Please use these to help
refine your learning, and please post any other questions you might have here!
Remember also that we only take the top 3 of 4 quizzes in calculating your final
Dave, Jan, Dana and Martyn
Q: Total internal reflection contributes to the brilliance of a gemstone by:
A: … returning light that enters through the crown and table of a gemstone back to
Q: Anisotropic minerals have:
A: …more than one refractive index along the crystallographic directions. The crystal
system of a mineral will define whether it is anisotropic or isotropic. An anisotropic
mineral can have either 2 or 3 distinct refractive indices, but they don’t necessarily
need to be very different. The monoclinic, orthorhombic and triclinic systems have 3
refractive indices. The tetragonal and hexagonal systems have 2 refractive indices.
Examples of anisotropic minerals include quartz, corundum, beryl, tanzanite, etc...
Isotropic minerals belong to the cubic/isometric crystal system and have only 1
refractive index, with important examples being diamond or garnet. This is important
for identification of gemstones, since identification of this property can rule out large
swaths of potential minerals. For example, moissanite is a diamond imitation (and a
good one!) but it has a hexagonal crystal system and is therefore anisotropic
whereas diamond has a cubic crystal system.
Q: Fluorescent lighting is can be problematic for selling items for which colour is a
selling factor, including gems, because:
A: the bulbs emit light irregularly across the spectrum, with spiked emittance at
several short wavelength segments, especially violet and green
Q: Internal reflection …
A: … is sought after when cutting diamonds and occurs when much of the light that
enters a cut gem is returned through the table to your eye.
Q: A translucent specimen ______.
A: … transmits less light than semi-transparent specimens. This one can be rather
intuitive – if you can look through the material (semi-transparent), it must transmit
more light than if you can only see that some light passes through (translucent).
Q: Which statement is true:
There are no more emerald deposits to be found, because every likely spot
where the geological environment is correct has already been checked. – Not
true, since we currently have an information on bedrock from a small part of Earth’s surface only (it is often covered by glacial sediments or other sedimentary
rocks, swamps, lakes, soil, etc.) and from a very tiny part of Earth’s crust interior
(which we can study in detail only in drill-cores or in underground mines).
Research on emeralds is always ongoing, but is hampered somewhat by the fact
that Be is notoriously difficult to analyze in a lab environment. – True.
Beryl grows best in high-pressure environments like the lower crust, where the
crystal is tightly packed on all sides during growth. – Not true, beryl forms in or
around granitic rocks or in hydrothermal system in low-pressureenvironments in
upper part of Earth’s crust.
Emerald deposits are easy to find because the two necessary geologic conditions
for most deposits, mafic rocks and felsic magmas, are always found together in
the same location. – Not true, these two rock types do not always occur next to
New deposits of highest-quality eme