lecture7 minerals

Minerals

Lithosphere: the Solid Earth

What’s below the surface:Rocks

But what’s inside a rock?

1 cm1 cm

Rock- Rock- a natural a natural aggregate of aggregate of mineralsminerals(and/or(and/ormineraloids)mineraloids)

Yes, but What’s a Mineral?

- a naturally occurring, inorganic, crystalline solid with a definite chemical composition and characteristic physical properties

e.g., quartz, diamond, graphite, talc

Mineral

Mineralogy= study of the composition, properties, &

classification of minerals (Geo 321- offered in Fall)

Minerals id’d by– crystal structure– hardness– luster– streak– color– density

What is a crystalline solid?

Are any inorganic solids not crystalline?

GlassGlass

How do we know a material is crystalline?Self-Similarity

HaliteQuartz

How do we know a material is crystalline?

X-ray diffraction

Chemistry of the Solid Earth

The Big 8 ElementsThe Big 8 Elements

O 46% -2

Si 28% +4

Al 8% +3

Fe 5% +2/+3

Ca 4% +2

Mg 3% +2

Na 3% +1

K 2% +1

Element Abundance Charge

99%

The Earth’s Crust

SiO2 - Quartz

Silica Tetrahedron SiO4

What is the charge?

Si = +4, O = -2 thus

-4

How can that be?

(Fe, Mg)2SiO4 - Olivine

How old are the oldest rocks on Earth?Given: Sample from Acasta Gneiss in CanadaIt has crystals of zircon thatcontain 238U.238U is unstable. It decays into 206Pb.

ZrSiO4

~Fixed chemical formula.

But a few U’s can be used To substitute for Zr.

How do Minerals Form?

- Cooling from liquid (magma) to a solid

How do Minerals Form?

- Evaporation of a briny liquid

- Cooling from liquid (magma) to a solid

How do Minerals Form?

- Precipitation from a fluid

Section of a pipe

Mineralized vein

- Evaporation of a briny liquid

- Cooling from liquid (magma) to a solid

Asbestos- fibrous silicate mineral w/ fireproofing qualities

Ceiling tiles

Asbestos- commercial term, not a geological term

Chrysotile- sheet structureno sharp fibres- no hazard

Crocidolite- chain structuresharp fibres- BIG hazard

The Cost- 50 to 150 billion $ to clean it all upThe Cost- 50 to 150 billion $ to clean it all up>half of the asbestos is harmless Chrysotile>half of the asbestos is harmless Chrysotile

What to Do?

What is a rock again?

= assemblage of minerals (or mineraloids) in a solid state

3 types7. igneous8. sedimentary9. metamorphic

Igneous

Sedimentary

Metamorphic

Plutonic Volcanic

1. Igneous rocks (fire-formed)= rock that solidified from a molten state

• majority of crustal rock (although it is often covered with sedimentary rocks)

• consists of silicate minerals w/ metallic elements

• “interlocking grains”e.g. granite, basalt, obsidian, pumice

Magma: molten rock beneath Earth’s surface

GraniteBasalt

ObsidianPumice