Mineralogy Lab 3 Specimen Questions: Name ________________ Pard _________________
Visual Appearance & Hand Specimen Optical Properties
1) Obtain specimens of the 2 relatively dense sulphide minerals Galena & Sphalerite. Note &
describe the luster, reflectance and internal reflections if any. Note & describe the crystal habit,
form & cleavage. Galena characteristically warps its cube faces as it cools off from hydrothermal
or nearly magmatic temperatures. Sphalerite with 6 cleavages has internal reflections when
viewed under a hand lens or binocular scope. For specimens with <10% Fe this looks like internal
fire or dragon’s eyes. Discuss the differences in these minerals & account for them by either
chemical make- up or crystal structure with special attention to electrons and light.
(14)
GALENA (PbS)
SPHALERITE (Zn,Fe)S
Luster
Reflectance
Internal Reflections
Habit
Form
Cleavage
Comparison
2) a-Obtain specimens of the 3 relatively low density minerals Talc, Muscovite and Gypsum.
Note & describe the luster, reflectance and internal reflections or refractions if any. Note &
describe the crystal habit, form & cleavage.
(21)
TALC
MUSCOVITE
GYPSUM
Formula
Luster
Reflectance
Internal Reflections
Habit
Form
Cleavage
Comparison
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b- Discuss the differences in these low specific gravity minerals & account for them either by
chemical make-up or crystal structure with special attention to electrons and light.
(4)
3) Obtain specimens of Calcic plagioclase feldspar (>50% CaAl2Si2O8 : Anorthite, Bytownite,
Labradorite) which exhibit labradorescence. Do non-destructive tests only! Draw any crystal
faces, cleavages, cut faces and twinning planes and relate these structures to the changes in
colour and quality of labradorescence. Draw an oriented specimen to show positions of
cleavages, albite twinning planes and best direction for viewing labradorescence (schiller, play
of colours from internal refractions at twin plane boundaries). Find the 2 “prismatic cleavages at
86° & 94°. Compare these hand specimens to the Albite (NaAlSi3O8 ) model.
(6)
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4) a-Using Ultraviolet lamps (don’t stare into them) examine the sets of Fluorescent minerals.
Compare and contrast the various colours, and intensities between Willemite, Franklinite &
other fluorescent minerals with more than 2 different specimens (2 fluorites, 2 calcites, 2
feldspars, 2 opals etc.). Comment on whether Fluorescence is an inherent or accidental property
for each mineral. Describe the colour in white light, long wave UV and short wave UV.
Substitute any other pair of variably fluorescent minerals: apatite etc.
(30)
Mineral
Colour (in white light)
Long Wave UV
Short Wave UV
Willemite
Franklinite
Fluorite 1
Fluorite 2
Calcite 1
Calcite 2
Feldspar 1
Feldspar 2
Opal 1
Opal 2
b-Discussion of fluorescence in minerals: Describe what happens when the fluorescent light is
turned off to the fluorescent colour. For larger ordinary specimens of: either Apatite, Calcite or
Fluorite from the brown boxes, find one that fluoresces and see if this persists in the streak.
Explain what it is in the mineral that causes fluorescence, structure or chemistry?
(6)
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5) Compare the magnetic properties of 2 cubic (or nearly cubic minerals) Magnetite & Pyrrhotite
with a hand magnet and discuss the difference. Hematite, is not magnetic. Can you find any
magnetic specimens of this? Explain. (Hint: try looking up their crystal structures in your books
or on line & compare where Fe and its partner atom sit in the structure each case. )
(9)
Mineral
Formula
Crystal System/Symmetry
Ferromagnetism?
Magnetite
Pyrrhotite
Specular Hematite
6) Obtain specimens of corundum which exhibit asterism. Label the relationship between the
“star” figure and the crystal structure on a drawing. Speculate on which crystal system or
systems might show such asterism, what one property must they all have in common? (8)
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