GEMS 331 EXAM QUESTIONS WITH ACCURATE
SOLUTIONS
Color in gemstones is often produced by ___. -- Answer ✔✔ All of them: Color
centers, absorption of specific light wavelengths, reflection of specific light wavelengths,
and impurities
A gem must be cut to specific dimensions because: -- Answer ✔✔ the index of
refraction will bend light only a specific amount.
Critical angle is -- Answer ✔✔ the angle, calculated from the refractive index, that
determines whether or not light is internally reflected
Reflection is ____ while refraction is ___. -- Answer ✔✔ when light bounces off the
surface of the gem, when light bends inside the gemstone
the most symmetrical crystal system is the ___ system. -- Answer ✔✔ Cubic
Something is crystalline if -- Answer ✔✔ the atoms in a solid are in a periodic
arrangement (Not all solids are crystalline. To be crystalline a material must be solid
AND have its atoms in a periodic arrangement. Opal is an example of a non crystalline
solid.)
,The angle at which light is completely reflected from the surface of a gem is ____. --
Answer ✔✔ Critical angle
(Normal: the normal is just a reference line - perpendicular to the surface that the light
is hitting.
Acute Angle: An acute angle is just an angle less than 90 degrees. There is no indication
given in the notes that this has to be an acute angle.
Snell's Law: This is the mathematical relationship between the refractive index and the
angle of incedence. This is independent of any specific angle at which light may strike the
surface.
Refractive Index: The refractive index is a measure of the speed of light in air versus that
of around a gem. It is not an angle in and of itself.
Critical Angle: This is the correct answer. The critical angle is "specifically the angle at
which total internal reflection occurs." Many of you were hung up on the word surface. I
recommend you look at a gem again. Or even look at a swimming pool. Internal
reflection occurs at the surface interface with the air. It is possible, and is the basis of
the definition, that the light is reflected from the surface of a gem. This is true
REGARDLESS of whether the light is coming above from outside, or below from inside
the gem.)
Which of the following is not a name for a variety of Topaz? -- Answer ✔✔ "brazil"
Ideally, true gemstones should be many things except ____. -- Answer ✔✔ synthetic
, Citrine is -- Answer ✔✔ a type of SiO2 containing Fe impurity often formed by heat
treatment of amethyst
If abundance at the surface of the earth were the only measure of value, what would be
the least valualble gem? -- Answer ✔✔ Amethyst (The more rare a gem, the more
valuable it would be. Of the gems listed, quartz is the most common. Since I clearly
stated that abundance is the only factor here, quartz would be the least valuable. The
other choices do not have any clear correlation with abundance.)
Olivine is found within ___ rocks, which are ___ in origin. -- Answer ✔✔ basalt,
igneous
Crystalline quartz has a hardness of ___. -- Answer ✔✔ 7
In the near future, a lunar mining expedition discovers a new mineral, Unobtanium. This
mineral displays many remarkable properties, not the least of which is it has a hardness
of 11 on Moh's scale. In order to form a gemstone out of this new mineral, what should
a gem cutter use to cut and polish the facets? -- Answer ✔✔ Anything harder than
quartz
Spodumene and Kunzite are varieties of what mineral? -- Answer ✔✔ Pyroxene
What color will red construction paper appear in blue light? -- Answer ✔✔ Black
The 6-pointed stars seen in certain rubies and sapphires are due to -- Answer ✔✔
numerous fine rutile needle inclusions in orientations at 60 degrees to each other (The
stars are due to rutile (TiO2) crystals in the ruby or sapphire. These crystals are parallel
to the hexagonal faces and thus in three orientations.)
SOLUTIONS
Color in gemstones is often produced by ___. -- Answer ✔✔ All of them: Color
centers, absorption of specific light wavelengths, reflection of specific light wavelengths,
and impurities
A gem must be cut to specific dimensions because: -- Answer ✔✔ the index of
refraction will bend light only a specific amount.
Critical angle is -- Answer ✔✔ the angle, calculated from the refractive index, that
determines whether or not light is internally reflected
Reflection is ____ while refraction is ___. -- Answer ✔✔ when light bounces off the
surface of the gem, when light bends inside the gemstone
the most symmetrical crystal system is the ___ system. -- Answer ✔✔ Cubic
Something is crystalline if -- Answer ✔✔ the atoms in a solid are in a periodic
arrangement (Not all solids are crystalline. To be crystalline a material must be solid
AND have its atoms in a periodic arrangement. Opal is an example of a non crystalline
solid.)
,The angle at which light is completely reflected from the surface of a gem is ____. --
Answer ✔✔ Critical angle
(Normal: the normal is just a reference line - perpendicular to the surface that the light
is hitting.
Acute Angle: An acute angle is just an angle less than 90 degrees. There is no indication
given in the notes that this has to be an acute angle.
Snell's Law: This is the mathematical relationship between the refractive index and the
angle of incedence. This is independent of any specific angle at which light may strike the
surface.
Refractive Index: The refractive index is a measure of the speed of light in air versus that
of around a gem. It is not an angle in and of itself.
Critical Angle: This is the correct answer. The critical angle is "specifically the angle at
which total internal reflection occurs." Many of you were hung up on the word surface. I
recommend you look at a gem again. Or even look at a swimming pool. Internal
reflection occurs at the surface interface with the air. It is possible, and is the basis of
the definition, that the light is reflected from the surface of a gem. This is true
REGARDLESS of whether the light is coming above from outside, or below from inside
the gem.)
Which of the following is not a name for a variety of Topaz? -- Answer ✔✔ "brazil"
Ideally, true gemstones should be many things except ____. -- Answer ✔✔ synthetic
, Citrine is -- Answer ✔✔ a type of SiO2 containing Fe impurity often formed by heat
treatment of amethyst
If abundance at the surface of the earth were the only measure of value, what would be
the least valualble gem? -- Answer ✔✔ Amethyst (The more rare a gem, the more
valuable it would be. Of the gems listed, quartz is the most common. Since I clearly
stated that abundance is the only factor here, quartz would be the least valuable. The
other choices do not have any clear correlation with abundance.)
Olivine is found within ___ rocks, which are ___ in origin. -- Answer ✔✔ basalt,
igneous
Crystalline quartz has a hardness of ___. -- Answer ✔✔ 7
In the near future, a lunar mining expedition discovers a new mineral, Unobtanium. This
mineral displays many remarkable properties, not the least of which is it has a hardness
of 11 on Moh's scale. In order to form a gemstone out of this new mineral, what should
a gem cutter use to cut and polish the facets? -- Answer ✔✔ Anything harder than
quartz
Spodumene and Kunzite are varieties of what mineral? -- Answer ✔✔ Pyroxene
What color will red construction paper appear in blue light? -- Answer ✔✔ Black
The 6-pointed stars seen in certain rubies and sapphires are due to -- Answer ✔✔
numerous fine rutile needle inclusions in orientations at 60 degrees to each other (The
stars are due to rutile (TiO2) crystals in the ruby or sapphire. These crystals are parallel
to the hexagonal faces and thus in three orientations.)
