EOSC 118 EXAM SET QUESTIONS
AND CORRECT REVISED ANSWERS
100% VERIFIED
8 most abundant elements in the Earth's crust from most, to least abundant: - Answer-
Oxygen, O 46.0
Silicon, Si 27.5
Aluminum, Al 8.0
Iron, Fe 5.0
Calcium, Ca 4.0
Sodium, Na 3.0
Potassium, K 3.0
Magnesium, M 2.0
Native elements - Answer- -When elements occur by themselves in rock (i.e., not
chemically bonded to other elements)
-20 elements can occur in their native state (not including gases); all are metals, semi-
metals, or non-metals, and are considered to be minerals.
-Ex: Au, Ag, Cu, and Pt
-Ex: Native non-metallic mineral: diamond (pure C)
Ex: Native semi-metallic mineral: arsenic (As)
Metal: (2 types) - Answer- 1. Base metals: when exposed to oxygen in the air will react
(or corrode) to form a metal oxide
2. Noble metals do not react to oxygen. This includes Au and Pt.
-They all have good electrical conductivity, good thermal conductivity, high densities,
malleability, ductility, and a metallic lustre.
-Weighed by mass (g)
The six crystal systems and the concept of crystal habits - Answer- -Crystal symmetry:
all crystals have symmetry and fall into 6 main groups: crystal systems
1.Cubic system: contains 3 axes at right angles and of equal length. Main form: cube,
octahedron and rhombic dodecahedron. Minerals include: halite, copper, and gold,
silver, platinum...
2.Tetragonal: contains 3 axes at right angles. Two are equal in length, third is shorter,
look like square prism
3.Hexagonal & Trigonal:3 crystallographic axes of equal length @120 degree to one
another and a fourth. Emerald, quartz
,4.Monoclinic:3 axes of unequal length, more minerals crystallize in this form than any
other
5.Orthorhombic:
6.Triclinic: least symmetrical shape of all.
-Crystal habits: the complete description of the external shape of a crystal
o Crystal faces, forms aggregates, appearance
The "ball and stick" and "polyhedral" methods for constructing atomic models of crystal
structures - Answer- -The building blocks of a crystal are what mineralogists call the unit
cell.
o Within that unit cell is a complex but highly
arranged collection of elements with an
intricate network of bonds that connect
anions and cations with remarkable symmetry
and order.
-Ball and Stick diagram: best diagram to view the structures
o The balls represent atoms and the sticks
represent chemical bonds
-The 3D shapes are called polyhedra and four of most common in minerals are the
tetrahedron, octahedron, cube, and icosahedron. These are also referred to as platonic
solid
Light as a wave: - Answer- -Light: wavelength, the distance from peak to peak or trough
to trough, and its frequency, the number of wave crests (or troughs) that pass through
one point in one second.
-Light emitting diode (LED) made to emit only one colour (monochromatic). In the case
of a red LED, there would only be light emitted with a wavelength in the ~650 nm range
and no light emitted anywhere else along the spectrum.
-Light sources that are not intended to be monochromatic can have widely different
spectral emittance curves depending on the composition of the source of energy we call
the "light bulb".
o These spectral emittance curves describe the intensity of light at a particular
wavelength
-This is why something you buy from a fluorescent-lit store (vegetables, clothes,
jewellery) might look a little different when viewed outside in natural daylight or in your
home under incandescent light.
o Businesses that depend on visual appearance to make their sales, such as in retail
sales of jewellery, are very much aware of this and usually consult lighting experts to
optimize conditions in their salesrooms.
Colour: - Answer- -The colour of an object is our eye's interpretation of light in the visible
spectrum
-ROYGBIV: reflect onto coloured surfaces we interpret
,-Ex: if 'white' light is shined on a surface that appears red to our eyes, then that means
electromagnetic radiation in the 'red region' is most effectively reflected
Subtractive colour theory to explain colour in minerals and gemstones (What is colour
L12 section 3) - Answer- - The colour that we see (wavelengths that are transmitted
through the gem and/or reflected from its surface) are complimentary to the colours
(wavelengths) that are absorbed in subtractive colour theory
o Ex: Gemstones are like "colour filters".
o Ex: If we subtract the yellow portion of the electromagnetic spectrum we look across
the diagram and will accordingly see a predominance of blue light. Similarly, if we
subtract yellow and cyan (i.e., green) we see a predominance of magenta (blue and
red) light. Conversely, if we subtract magenta (blue and red) we see green.
- Incident light coming from the left interacts with coloured filters and 'exits' to the right
as either blue, green, or red light
Reflection: - Answer- -When light passing through one medium strikes another medium,
part of that light is reflected (like a mirror) and the other part is refracted (like what you
see through a fish tank).
o Angle of incidence is equal to the angle of
reflection (<i = <r).
Refraction: - Answer- -When light passes from one medium into another, its speed
changes causing light to "bend" or change in direction. The degree to which light is
slowed and bent relate to the differences in the refractive indices between the two
media as well as the angle at which the light path makes with the medium.
-Light rays that pass from one medium to another (at angles other than 90 degrees)
undergo refraction and that the degree of refraction of light is dependent on its
wavelength.
Refractive index: (isotropic and anisotropic) - Answer- -Measures how much the incident
light is slowed when it enters a new medium compared to when it travels in a vacuum
(where the refractive index is, by definition, equal to 1)
-Isotropic and anisotropic minerals
o Examples of isotropic minerals with a single refractive index are diamond (n=2.419)
and spinel (n=1.725). Material from all crystal systems other than isometric show more
than one refractive index and are termed anisotropic.
o Isotropy and anisotropy are very useful in identifying gemstones. With the proper
observations many different species can be ruled out using this physical property of a
gemstone.
-ex: The doubling of text and gem facets
, Total internal reflection: - Answer- -Important to consider for faceted gemstones. When
light travels from a medium with high refractive index (gemstone) to one with low
refractive index (air), total internal reflection can occur if the angle of incidence is
greater than the critical angle.
-Critical angle:
o The critical angle defines the angle of incidence above which total internal reflection
occurs.
o Particularly significant in diamonds, which have a high refractive index of 2.419, are
faceted with specific angles and proportions to maximize the amount of light that
undergoes total internal reflection.
Dispersion: - Answer- - "White" light is a mixture of light with wavelengths across the
visible range. Thus when white light enters or leaves a material at angles other than 90
degrees, individual spectral wavelengths (colours) will be refracted by different
amounts.
- Longer wavelengths (e.g., red) are refracted the least and shorter wavelengths (e.g.,
violet) are refracted the most. This phenomenon of dispersion is what gives gemstones
their fire.
Chain of Custody Principle - Answer- - Each component and step leading to a finished
piece of jewellery is tracked and documentation.
- This principle ensures assessment and accountability of the practices engaged in. The
concept of tracking is sometimes referred to as Mine to Market. (ex: Wal-Mart tracking)
- Kimberly Process only applies to gemstones, not entire pieces of jewellery.
The Responsible Jewellery Council (RJC): - Answer- - Organization who's members
"are independently audited against the
o The Code of Practices addresses human rights, labour rights, environmental impact,
mining practices, product disclosure and many more important topics in the jewellery
supply chain. RJC Members are grouped into 7 Forums representing different parts of
the diamond, gold and platinum group metals jewellery supply chain.
o "Conflict Free" into 5 portions of conformance:
1. Conflict Assessment
a. Whether there is conflict near the producing mine
2. Company Assessment
a. Whether the company operates in a broader conflict region
3. Commodity Assessment
a. Whether the company can move its commodity safely, such as across a conflict
region
4. Externally Sourced Gold Assessment
a. Whether the company acquires gold from outside the mine site, to ensure it is conflict
free
5. Management Statement of Conformance
a. Whether the company formally states conformance to the above variables
