Minerals I Elements of the Earth’s crust
Properties of mineralsCrystal form
Cleavage/Fracture
Color, streak, luster
Hardness, tenacity
Specific gravity
Acid test, magnetism, etc.
http://www.nps.gov/seki/snrm/geology/cave_photos.htm
Why Study Minerals?
Building blocks of Earth materials
Economically important
Essential to understanding rock formation
Minerals are cool
naturally occurring - materials synthesized in laboratory do not count, must be formed by natural processes in wild
inorganic - not formed by organic chemistry (e.g., sugars, etc.)
homogeneous solid - single substance in solid phase which cannot be physically separated into simpler compounds
definite chemical composition - composition can be represented as chemical formula (e.g., NaCl), although variation in exact composition is possible (e.g., (Mg, Fe)2SiO4 )
ordered atomic arrangement – repeating structure at the atomic level, which expresses as symmetry in large specimens, i.e., crystalline structure.
http://www.uoregon.edu/~jrice/geol311
Mineral - A naturally occurring, inorganic, homogeneous solid with a definite chemical composition and an ordered atomic arrangement.
Mineral FormationMinerals found at the Earth’s surface formed from natural
processes both within the Earth and at the Earth’s surface. Environments vary greatly, and include:
High temperature and pressure typical of the upper mantle.
Evaporation basins
Ocean bottoms
Volcanic calderas and lava flows
A host of stressful environments in mountain building zones
And thousands of others!
Mineral Properties
Crystal Form
Cleavage/Fracture
Color
Streak Color
Luster
Crystal Form
Cleavage/Fracture
Color
Streak Color
Luster
Hardness
Tenacity
Specific Gravity
Acid Test
Magnetism
Hardness
Tenacity
Specific Gravity
Acid Test
Magnetism
Most useful properties for mineral identification
Mineral Properties
Crystal Form• Cleavage/
Fracture• Color• Streak Color• Luster
Crystal Form• Cleavage/
Fracture• Color• Streak Color• Luster
• Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
• Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
Crystal symmetry is controlled by the atomic structure of mineral
4-fold axes (90o)
90o
Symmetry
4-fold symmetry (90o)
http://www.a-m.de/englisch/lexikon/mineral/halogenide/halit-bild1.htm
3-fold symmetry (120o)
3-fold axes (120o)
Symmetry
http://home.planet.nl/~bartdw/sphalerite.htm
Crystal FormThere are only 6 symmetry classes; each mineral belongs to only ONE
symmetry class, and thus all crystals exhibit that symmetry only!
http://members.aol.com/jmichaelh/part1.html
isometric tetragonal orthorhombic
hexagonal monoclinic triclinic
Crystal FormCaveat One: Crowding of other crystals can mask symmetry
Caveat Two: Crystals are often too small to see
Symmetry can always be seen using techniques like X-ray diffraction
Mineral Properties
• Crystal Form
Cleavage/Fracture
• Color• Streak Color• Luster
• Crystal Form
Cleavage/Fracture
• Color• Streak Color• Luster
• Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
• Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
Cleavage - tendency to split along planes of weakness corresponding to weaker chemical links in internal structure of crystal
A single crystal can display several cleavage directions.
The cleavage directions are not always at right angles to each other. They also are not necessarily parallel to the crystal faces of the mineral.
1 direction 2 directions
Cleavage
Can be parallel to crystal faces, but is often at an angle
Parallel Cleavage
Fig. 02.19a
One Direction of Cleavage
One Direction of Cleavage
Fig. 02.21
Two Directions of Cleavage
Three Directions of Cleavage
Fig. 02.22http://www.geology.sdsu.edu/visualgeology
http://www.greatsouth.net/http://www.xpsdata.com/
Fluorite Crystals
Four Directions of Cleavage
Mineral Properties
• Crystal Form
Cleavage/Fracture
• Color• Streak Color• Luster
• Crystal Form
Cleavage/Fracture
• Color• Streak Color• Luster
• Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
• Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
Fracture - any breakage that is not cleavage
conchoidalfracture
Characteristic of quartz, chert and flint
Fig. 02.23
conchoidal fracture
Mineral Properties
• Crystal Form• Cleavage/
Fracture
Color• Streak Color• Luster
• Crystal Form• Cleavage/
Fracture
Color• Streak Color• Luster
• Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
• Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
Characteristic for some minerals, useless for most
SpinelMgAl2O4
Hardness = 8
One mineral can come in a rainbow of colors
QuartzSiO2
Hardness = 7
Rose QuartzRose Quartz
SmokeyQuartz
QuartzCitrine
AmethystAmethyst
Carnelian
OnyxJasper
Alexandrite
sunlightsunlight
artificiallight
artificiallight
One mineral can appear to be different colors under different lighting
BeAl2O4
Hardness = 8.5
Chrysoberyl
Mineral Properties
• Crystal Form• Cleavage/
Fracture• Color
Streak Color• Luster
• Crystal Form• Cleavage/
Fracture• Color
Streak Color• Luster
• Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
• Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
Streak Color - Color of powdered mineral, which may or may not be the color of the crystal
hematite streak color
Mineral Properties
• Crystal Form• Cleavage/
Fracture• Color• Streak Color
Luster
• Crystal Form• Cleavage/
Fracture• Color• Streak Color
Luster
• Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
• Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
Luster - quality of light reflected from mineral surface
Luster - quality of light reflected from mineral surface
metallicpyrite
gold
silver
Luster quality of light reflected from mineral surface
resinouspearly
vitreous (glassy)non-metallic
Mineral Properties
• Crystal Form• Cleavage/
Fracture• Color• Streak Color• Luster
• Crystal Form• Cleavage/
Fracture• Color• Streak Color• Luster
Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
Hardness• Tenacity• Specific Gravity• Acid Test• Magnetism
Hardness - resistance of mineral to scratching or abrasion
Mohs Hardness ScaleAustrian mineralogist F. Mohs, 1824
Based on relative hardness of 10 common minerals
Based on relative hardness of 10 common mineralshard
soft
10. Diamond C9. Corundum Al2O3
8. Topaz Al2SiO4(F,OH)2
7. Quartz SiO2
6. Orthoclase KAlSi3O8
5. Apatite Ca5(PO4)3(F,Cl,OH)4. Fluorite CaF2
3. Calcite CaCO3
2. Gypsum CaSO4
1. Talc Mg3Si4O10(OH)2
Higher numbered minerals scratch lower numbered minerals
fingernailcopper penny
glass plate
Fig. 02.14
Muscovite
Hardness < 2
Can scratch with fingernail (H=2.5)
Muscovite
Hardness < 2
Can scratch with fingernail (H=2.5)
Fig. 02.15c
Fluorite
Hardness =4
Can scratch copper penny (H=3.5), but not glass plate (H=5.5)
Fluorite
Hardness =4
Can scratch copper penny (H=3.5), but not glass plate (H=5.5)
Fig. 02.15b
Apatite
Hardness =5
Can scratch copper penny (H<3.5), but not glass plate (H=5.5)
Apatite
Hardness =5
Can scratch copper penny (H<3.5), but not glass plate (H=5.5)
Fig. 02.15a
Quartz
Hardness =7
Scratches glass plate (H=5.5). Hardest of common minerals
Quartz
Hardness =7
Scratches glass plate (H=5.5). Hardest of common minerals
Mineral Properties
• Crystal Form• Cleavage/
Fracture• Color• Streak Color• Luster
• Crystal Form• Cleavage/
Fracture• Color• Streak Color• Luster
• Hardness
Tenacity• Specific Gravity• Acid Test• Magnetism
• Hardness
Tenacity• Specific Gravity• Acid Test• Magnetism
Tenacity - resistance of the mineral to breaking
• Crystal Form• Cleavage/
Fracture• Color• Streak• Luster
• Crystal Form• Cleavage/
Fracture• Color• Streak• Luster
• Hardness• Tenacity
Specific Gravity• Acid Test• Magnetism
• Hardness• Tenacity
Specific Gravity• Acid Test• Magnetism
Specific Gravity - density of the material (g/cm3)
Mineral Properties
Specific Gravity
Related to both the atomic weight of the contained elements, and how tightly the atoms are packed
Orthorhombic CarbonatesAll minerals have same structure, only cation differs
Mineral Formula Cation g/cm3
Aragonite CaCO3 20 2.95
Strontianite SrCO3 38 3.76
Witherite BaCO3 56 4.29
Cerrusite PbCO3 82 6.55
Specific Gravity
Related to both the atomic weight of the contained elements, and how tightly the atoms are packed
Both are minerals composed of the element carbonGgraphite = 2.23 (loose)Gdiamond = 3.51(tight)
http://geology.uvm.edu/vtlandforms/gl_graph.htmhttp://geology.uvm.edu/vtlandforms/gl_graph.htm
Graphite Diamond
Mineral Properties
• Crystal Form• Cleavage/
Fracture• Color• Streak• Luster
• Crystal Form• Cleavage/
Fracture• Color• Streak• Luster
• Hardness• Tenacity• Specific Gravity
Acid Test• Magnetism
• Hardness• Tenacity• Specific Gravity
Acid Test• Magnetism
Reaction to dilute acid; especially useful in identifying carbonate minerals
Minerals like calcite react with weak acid, dissolving the mineral and producing lots of bubbles (effervescence)
Mineral Properties
• Crystal Form• Cleavage/
Fracture• Color• Streak• Luster
• Crystal Form• Cleavage/
Fracture• Color• Streak• Luster
• Hardness• Tenacity• Specific Gravity• Acid Test
Magnetism
• Hardness• Tenacity• Specific Gravity• Acid Test
Magnetism
Some minerals strongly attract magnets. Characteristic of magnetite and some other minerals