minerals i elements of the earth’s crust properties of minerals crystal form cleavage/fracture...

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/


• 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




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


• Crystal Form

Cleavage/Fracture




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


Fracture

Color• Streak Color• Luster



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


Fracture• Color

Streak Color• Luster


Fracture• Color

Streak Color• Luster



Streak Color - Color of powdered mineral, which may or may not be the color of the crystal

hematite streak color

Mineral Properties


Fracture• Color• Streak Color

Luster


Fracture• Color• Streak Color

Luster



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





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





• Hardness

Tenacity• Specific Gravity• Acid Test• Magnetism

• Hardness

Tenacity• Specific Gravity• Acid Test• Magnetism

Tenacity - resistance of the mineral to breaking


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





• 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





• 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

minerals i elements of the earth’s crust properties of minerals crystal form cleavage/fracture...

Documents

cleavage directions

atomic structure of

symmetry classes

fold symmetry 120o3fold

mineral formationminerals

single crystal

crystal faces

angleparallel cleavage