earth science3
ademola
Aug31_minerals_density3.pptxGiven 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
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) | Displacement 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.
