Quiz 3 review
Good job on Q3! The average was about 16.2, please, find below a
discussion on some of the most commonly misanswered questions on
Quiz 3. Don't hesitate to continue asking questions!
Dave, Jan, Dana and Martyn
Q: The specific gravity (or density) of corundum is:
A: … fairly dense (~4.1 g/cm3) compared to the average density of
the upper crust (~2.6 g/cm3) and therefore the minerals that it
comprises. This is the reason that we can recover corundum in placers
whereas minerals like beryl (density of ~2.7) usually just get washed
down the rivers along with most other materials.
Q: Ruby gets its colour from which substitution in the crystal
structure of corundum:
A:… ruby is the result of Cr substituting for Al in the crystal structure
of corundum (Al2O3), and to the tune of about 1% weight
percent. For keen students, an interesting study looking at the
provenance of rubies was done by Garnier et al (2002) and looked
primarily at Cr and Fe contents (search Google Scholar for “Trace
element contents and cathodoluminescence of “trapiche” rubies from
Mong Hsu, Myanmar (Burma): geological significance”).
Q: Modernmined corundum is mostly not of gem quality; _____% of
gemquality rubies and sapphires are untreated.
A: Quality of corundum is really low correct answer is that only 1%
of the gemquality rubies and sapphires are untreated.
Q: How could you tell the difference between a rough Maxixe stone
and a rough Kashmir sapphire?
A: This was a bit of a tricky one, aimed to test the knowledge that
Maxixe is a dark blue gem variety of beryl whereas Kashmir sapphire
is a velvety blue gem variety of corundum. The main differences are in shape of the rough stone, controlled by the identity of the parent
mineral Kashmir sapphire (corundum) generally has tapered ends
whereas Maxixe beryl will form hexagonal prisms with flat
terminations. Also, corundum is harder than beryl.
Light and Optics
Q: How does fluorescence in minerals work?
A: Atoms moved to a higher energy (“excited state”) by UVlight drop
back to their “ground state” by releasing energy as visible light. The
light that can shift the atom to the excited state has typically high
frequency (UVligh, Xrays) and the energy is then (when going back
to ground state) released as a visible (fluorescent) light at lower
Q: Which of the following phrases will make this statement TRUE?
The Chelsea Filter____.
A: is a colour filter that filters out any blue hues of light
Pegmatites and Other Gems
Q: Imagine a large magma body (or cooled intrusion) and a field of
related pegmatites surrounding it in all directions. Where would you
expect to find the LEAST number of gems?
Q: All pegmatites are initially generated in larger parent magma
bodies or intrusions. In general, how far away does a pegmatite have
to be from the larger parent magma body (or intrusion) to have high
concentrations of unusual or rare elements (e.g., Li)?
A: These two questions