Science

Given a random pile of stones- how would you sort them?

What classification system would you adopt?

Given a random pile of stones- how would you sort them?

What classification system would you adopt?

My favorite: purity All one composition

Rocks and Minerals I

http://www.geology.wisc.edu/~maher/air/air14.htm

What distinguishes rocks from minerals?

 Composition A mineral is a homogeneous solid and has a fixed composition. It is formed through natural processes and is usually inorganic. It has a defined crystal structure (glass is not a mineral. Its pure, but does not have a crystal structure- more on this next time).

John Veevaert

John H. Betts

What distinguishes rocks from minerals?

 Composition A rock is heterogeneous and formed from two or more minerals. Andrew Alden

http://www2.vscc.cc.tn.us/svinson/ geo100/sedimentary.html

So my favorite characteristic for sorting the piles, is purity. (recognizing that it doesn’t cover glass). But it is generally good for distinguishing rocks vs. minerals.

Might have noticed that the pure specimens tended to be smaller

Minerals

 Let’s take a look at some of the characteristics of minerals and their tests.

Mineral Formulas A mineral has a definite chemical formula such as: NaCl, called halite; CuAl6(PO4)4(OH)8·4(H2O), known as turquoise; or (K(Mg,Fe)3AlSi3O10)(OH)2) which is biotite.

Don’t worry about the details of these complicated formulas!

Mineral Color Color alone is not the best identifier of a mineral. This is related to part of the homework “fools gold” looks “gold”.

Patrick Laird

Patrick Laird

Floyd Hawk

Mike Streeter

Mineral Streak The powdered color

of a mineral is characteristic. You can see the color by dragging the mineral across a rough surface. The result is called a streak.

Patrick Laird

http://geology.csupomona.edu/alert/mineral/streak.htm

Mineral Luster Mineral luster

is a term for describing the way light is reflected from the surface of a mineral.

Lusters: metallic

shiny dull

non-metallic adamantine earthy pearly silky greasy resinous glassy

Galena - metallic

Spodumene – glassy http://webmineral.com/specimens/picshow.php?id=1091

http://webmineral.com/data/Galena.shtml

Mineral Hardness Hardness is a

mineral’s resistance to being scratched. A harder mineral will scratch a softer one. Hardness is a relative measure and is assigned a number based on the Mohs Scale.

www.yuprocks.com

Lou Perloff

Diamond hardest

Talc softest

Mineral Hardness Hardness

(Mohs) Mineral Some familiar

objects 1 Talc (Mg3Si4O10(OH)2)

2 Gypsum (CaSO4·2H2O) Fingernail: 2.5 Gold or silver

2.5-3

3 Calcite (CaCO3) Copper penny: 3 4 Fluorite (CaF2)

5 Apatite (Ca5(PO4)3(OH-,Cl-,F-)) Regular knife

blade 5-6

6 Orthoclase Feldspar (KAlSi3O8) Glass: 5-7

7 Quartz (SiO2) Hardened steel file: 7” 8 Topaz (Al2SiO4(OH-,F-)2) 9 Corundum (Al2O3)

10 Diamond (C)

Try and scratch gypsum

Other Mineral Properties: Chemistry

http://geology.csupomona.edu/alert/mineral/other.htm

http://www.yourgemologist.com/magnetite.html

Some carbonate (they must have CO3 as part of their formula) minerals react to an acid such as HCl. The reaction produces carbon dioxide gas which will “fizz” on the mineral surface.

Some minerals show magnetism or are attracted to magnets. Magnetite is the best example and has been used to make magnets. Has iron (Fe) and oxygen (O)

All minerals have a density Density: amount of matter in a given volume of the substance.

D=M/V

M: mass (related to weight). Typically expressed in grams (gm) or kilograms (kg). A kg is a bit over 2 pounds. A gm is less than 1 ounce.

V: volume. Typically expressed in cubic centimeters (written either as cc or as cm3) or cubic meters (m3) .

Densities that are high or low may be helpful in identifying the mineral.

How can we measure density? Two steps

How can we measure density?

Step 1: find the mass  weigh your sample on a scale Answer will be in grams (If desired, can convert 454 grams per pound, but

densities are typically given as gm/cc)

Step 2: find out how big it is (the volume)  use water displacement method (next slide) (also Section 5.3 of text covers this but in more detail than we need)

Measuring volume- the water displacement method

1. Fill beaker partway with water- measure the water level the answer is in milliliters (ml) which conveniently happen to equal cubic centimeters (cc) 1 ml = 1 cc

2. Plop your sample in- what happens to the water level?

3. Measure the water level again

Displacement = final volume – initial volume = volume of sample

Put it all together mass of sample

Density = ---------------------- final volume – initial volume

Instructor Demo: measure density of quartz, olivine, hematite (why these three minerals?........ Stay tuned)

Specimen Mass (gm) Initial water volume (ml)

Final water level (ml)

Displaceme nt volume (ml) (final-initial)

Density measured (actual) gm/cc

Quartz 76 95 125 30 2.5

Olivine 85 95 120 25 3.4

Hematite 100 95 113 18 5.55

If you know two of three (mass, volume (i.e displacement), density), you can always find the third.

Why those three minerals?

Quartz: composed of Silicon and oxygen SiO2 Si and O are the most common elements in earth’s crust Combination called “silica”. Quartz is pure silica. So is (often) beach sand

Other common minerals are silica + some metal  called silicates.

Olivine: A silicate often bound up with iron. Iron is very dense which is why olivine is more dense than pure silica

Hematite: not a silicate. Combination of iron and oxygen. Extra presence of ion makes this the densest of the three.

These three elements: Iron (symbol Fe), Silicon, and oxygen are the Most important elements to know for the solid earth.

1. Oxygen: most common element earth’s crust 2. Silicon: #2 most common in earth’s crust (always bound w/ oxygen) 3. Iron: tied with oxygen for most common element in whole

earth, but most of it is deep down towards the earth’s center. Less (but some) in crust

1. Oxygen: Part of air, water and solid earth, most common in rocks we see

2. Silicon: #2 important for rocks we see, combines with oxygen to make silica

3. Iron: Most important for deep within the earth. Densest of these 7.

4. Carbon: combines with oxygen carbonates in rock (acid test), carbon dioxide in air (plants use)

5. Hydrogen: part of water, simplest element, most common element in universe

6. Helium: #2 most common in universe, #2 simplest

7. Nitrogen: most common constituent of the air (not oxygen!)

For rocks and minerals we’re only interested in 1-3, altho 4 is present

Elements you will encounter in this course (and need to know)  The Magnificent Seven!

Getting ready to mix minerals together.

Lets just summarize mineral properties

Color: not as reliable due to effects of small impurities Streak: color of powered form Luster: reflectivity Hardness: resistance to scratching Density: reflects chemical composition  important

for rocks Reactivity to acid- useful for chemical compositon Magnetism?  can tell you if you have iron (high density)

Consider combinations of minerals (i.e. rocks)

To combine, we melt. We then get …………?

Where does the heat come from to melt?

Magma (molten material underground) Lava (molten material on the surface)

Only two sources of heat for the earth 1. the sun (not hot enough to melt rock/minerals) 2. the earth’s deep interior

So melting of the solid earth occurs underground where the temperature is hotter. This produces magma. Note: a misconception- the earth underground is not always molten

It depends upon other factors like the pressure

Magma will have different densities depending upon the mixture of minerals

What happens when you mix liquids of different densities? (or a solid and liquid when they are different densities).

See demo with olive oil, ice cube, plain water

Melting different combinations of minerals

Density of Olive oil = 0.92 gm/cc

Density of Ice = 0.93 gm/cc

Density of Water = 1.0 gm/cc

Fun website (if you have adobe flash) https://phet.colorado.edu/sims/density-and-buoyancy/density_en.html

Buoyancy: less dense floats above more dense

What happens when a liquid is cooled and solidifies?

ice  freezes

More rigorous term crystallization

What happens when magma crystallizes?

you get igneous rock, the first of the 3 main types of rock Different types of magma  different types of igneous rock with different

densities

Two types of igneous rock Silica rich magma (i.e. ½ pure quartz, no iron, some other lighter metals):

forms granite Density about 2.6-2.7 gm/cc

Silica poor magma (i.e. has silicates, but no pure quartz, more metals including iron from melted olivine): forms basalt Density about 2.9-3 gm/cc

Since silica has a lower density than iron, granite is lower density than basalt. Silica also melts more easily and crystallizes more slowly

Section 20.7 of text: two categories of igneous rock basalt  crystallized lava (surface or ocean floor) granite  crystallized magma below surface

Silica rich vs. silica poor (fig 20.13 in text)

Silica-poor (forms basalt)

Silica-rich (forms granite)

Melting temp Order of melting

HIGH

LOW

LAST

FIRST

Order of crystallization

This is how magma can generate different Igneous rocks- the silica-poor stuff crystallizes first, sinks and lets

the silica-rich magma flow upwards

LAST

FIRST

Granite “floats” on top of basalt Granitic magma stays liquid longer. Is less dense

 “floats” higher than basalt (see Section 5.4 of text on buoyancy picture of floating

mountains)

Basalt  Oceanic Crust (bottom of the sea floor)

Granite  Continental Crust which sits on top of basalt

In our ordinary daily life, what kind of igneous rocks will we usually see?

Basalt is most common igneous rock, but harder to see on earth’s surface. So whats the

best way to see it?

Summary

Minerals and their properties

How density can vary, can be measured and can be used to understand mixtures of minerals.

Lays foundation for understand structure of earth’s outer shell, the crust.