Jessica Zhao
Geology, p6
10/28/10
Geology Notes #3
(10/12 to 10/27)
ASTRONOMY
Dwarves:
white – old, dead main sequence stars
red – smallest, barely there stars, not bright, long lifetime
brown – no fusion (except deuterium, but not much in universe); giant planets, almost
stars
yellow – small ordinary mainstream stars, common, yellow (ex: our sun)
black – after white dwarves cool off (none exist yet)
Type 1A Supernovae
- Always form from white dwarves slightly over mass
- All same brightness, therefore good standard candle
- Explosion takes seconds; light gets reemitted for a while before it starts traveling
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Only 1 galaxy moving towards us (Andromeda), all others red shift
Brightest spectral lines: hydrogen
In a few billion years, Milky Way and Andromeda will collide  Starburst!
Starbust = burst of star formation; star dust collides and forms other stars; this is bad,
many hot, young stars form that will become supernovae
Strong linear correlation between Red Shift and distance to galaxy, slope of line is
Hubble’s constant
Why? We are center of universe OR maybe there isn’t a center, therefore, universe is
expanding
Astronomers consider everything not hydrogen/helium to be metals; can’t form solids
out of hydrogen or helium
Earth: Iron core, with silicon, oxygen, nickels
Sun: mostly silicon and oxygen
When a star gets a core of Iron 56, explosion! Outer shell gets blasted off; several
solar masses blasted  turns to elements and makes other bodies, emits x rays and
gamma rays
Technetium: Element 43; wasn’t discovered for some time because all isotopes are
radioactive
Earth has iron-nickel core: how do we know? – magnetic poles, and studying
meteorites
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Primitive meteorites (Carbonaceous Chondrites) look like they haven’t been changed
since creation of solar system (heated, cooled, etc); good example of raw solar system
material; Earth has similar composition
Technetium is rare, so in these meteorites we can study decay, therefore figure out
age of solar system
Creation of Star: star starts fusing from clump
Light pressure: not much effect on earth
Surface area/volume
Clears out dust and particles
Larger effect on small particles vs. big particles
Dust blocks sight; dust absorbs light and reemits it as infrared
Objects at normal temperature give off infrared, very difficult for ground based
telescopes to distinguish from this and from space
Technically, infinite time for dust to gather; but there’s a shock wave/compression
wave that compresses gas, then that compresses more, etc
Star formations usually occur in open clusters
Our solar system probably formed from different supernovae, violent
Temperature difference between inside and outside of solar system
Volatility: how easy it is to vaporize
Most volatile: CH4, N2 NH3 CO2  H2O  alkali metal-rich silicates (1st column)
 other silicates/metals
Refractory: opposite of volatile
Earth is densest in solar system, mercury comes next
Earth can’t hold helium, it goes into space; least renewable resource
Beginning of Earth: NO helium; it comes from contamination of natural gas,
radioactive decay of uranium
Earth largest of terrestrial planets
Critical size threshold that Earth did not reach to hold helium
Saturn: ¼ of Jupiter
Beginning of Earth: lots of molten rock, cools down, things calmed down
Late Heavy Bombardment: bombardment of comets, asteroids, result of Jupiter
screwing up everything
possible there was life before, then destroyed
Jupiter
runaway mass; silicon and iron core; attracts many asteroids; large storms; metallic
hydrogen forms most of composition
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Great Red Spot: cyclonic storm, much like a hurricane on Earth; has persisted for
hundreds of years
Red layers of ammonium
Very recently, one of big stripes has vanished
Saturation: when things are brighter in background (ex: hard to take picture when sun
is in the background)
Trapezium Cluster: (Theta Orionis), lit up by 4 bright stars in center; cluster of many
extremely young bright stars that will turn supernova, these light/heat up surrounding
gas
Most nebulae mistaken for planets before because they all looked like fuzzy blue
balls
M57 – Ring Nebula: visible from LA, gives off layer of gas from dead star
Cat’s Eye Nebula
Eagle Nebula
M42 – Orion Nebula; winter constellation, open cluster; in pictures, usually blurred
because of nature of nebulae
Probes
1. Solar-powered
pro: perpetual, hard to break
con: don’t get much power; also, less power as you go out further; dust
2. Thermo nucleic electronic generators
- plutonium cores, leftover from Russia/Cold War supplies
- heat generates electricity
- Other rovers: meters per day; these can move a mile/ hour! – much faster than
solar powered
Con: unstable, not firmly established
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M1: Crab Nebula
Written records from Chinese astronomers in 1054 that star blew up
Really bright, can be seen during day
Now remnants of supernova
Light Echo: supernovae visible from existing gas today that’s traveling toward us
Planetesimals: Mini-planets
Things start sticking together by gravity, chemical reactions with ions
Initially, process is insubstantial because they’re small objects
As it gets larger, gravity increases, it generates heat (from explosions btwn objects
that warms it)
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Threshold when it starts melting metals
Specific Density:
How density compares to water’s density (1)
Normal rocks have density of 2.5-3.5
Rock is easier to heat than water
Energy for formation of Earth enough to kill Earth (which probably did happen)
Molten Earth: dense stuff went down, other stuff went up
Cool crust of basalt/silicate-ridge
Metals sank down to core
Top: least dense
Differentiated body – sorted into layers
If we find meteorites with crust material (basalt), it must have come from something
larger (a differentiated body)
Iron meteorites, pallicites (really pretty): sliced and cleaned, made into jewelry
Earth’s core: all things rare at crust are here, like uranium, platinum, and other crazy
metals
Difficult to mine; alternative? – mine asteroids
Related Words:
Asteroid: A BIG rock in space
Meteoroid: a random rock in space
Meteor: shooting star; can be rock, sand, or solid something; falls through sky – fireball! usually
burns up in atmosphere
Meteorite: when a meteor is on the ground; rare because they’re hard to find; fraction of ironnickel meteorites rare (metal detectors); non iron-nickel ones are usually found in Sand Dunes
(obvious) and Antarctica
Comet: frozen mass that travels around the sun in a highly elliptical orbit
Earth
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Beginning, dry Earth (because of high temperature, things go to atmosphere, like
water)
Most water in oceans came from comet collisions
Moon probably generated with giant collision between Earth and a Mars sized thing
(10% mass of Earth), or 2 planet sized things
ROCKS AND MINERALS
Minerals vs. Rock
- Mineral: 1. something with a fixed chemical composition/formula 2. Crystal structure
3. Naturally occurring
- Rock: not really any formal definition; anything that’s hard (minerals are rock, by
definition)
- About 10-20 minerals that make up most rocks; people discover new minerals that are
microscopic
Examples:
Granite: easy to pick out minerals, course-grained
Quartzite: whitish, made only out of 1 mineral (quartz)
Marble and Chalk: both made out of single mineral (calcite), but they don’t behave the same way,
not formed the same way
Obsidian: volcanic glass; it’s a rock but not made of minerals
- glass is not a mineral because no crystalline structure (it is amorphous)
Basic properties of minerals
1. Chemical Formula
2. Naturally occurring
3. Crystal structure: different geometric shapes (cubes, hexagons)
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if you let something grow without interference, it will have clear,
geometric shapes of crystals, with crystal faces
different shapes called crystal habit: the ideal geometric shape it’ll take on
but, usually not ideal conditions; the grains aren’t perfect because of
external factors
thus, perfect crystals = $$$
diamonds formed with pressure on carbon; CVD (Chemical Vapor
Deposition)
can artificially make perfect diamonds, rubies, emeralds, etc. but NOT
alexandrite (different colors from various angles)
Crystal Faces: perfects, smooth surfaces
Examples:
Watermelon Tourmalline: results from subtle changes in trace ions
Other distinctive traits: color, crystal habit, hardness, cleavage/fracture, lustre, streak
Hardness:
- Based on if one mineral can scratch the other
Mohs Hardness Scale (German)
1- Talc (soft, common, in baby powder)
2- Gypsum (raw component in plaster, drywall)
[Fingernails]
3- Calcite (most common)
4- Fluorite (pretty crystals, main ore of fluorine)
5- Apatite (usually microscopic, main ore of phosphorus)
[Typical steel, like knives]
6- Orthoclase (Pink stuff in granite)
7- Quartz
8- Topaz
9- Corundum
10- Diamond
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Quartz - 7
trace contaminants make different colors
smoky quartz: radiation damage
pure quartz is opaque (can’t see through it), because light refracts off
hardest common mineral
things with 7 and above difficult to scratch
most watches have a synthetic sapphire glass
easy to confuse gypsum/calcite, but use fingernails to scratch gypsum
Calcite vs. Quartz: use knife
Corundum: name for many gemstones, but just different colors
 99.9% same chemical composition
 Most sapphires are light blue (barely)
 Most deep blue sapphires are rare, and artificial ones are made through heat
 Star Sapphires: light shines for star pattern, RARE = $$$
Cleavage:
- Based on chemical structure, determines which direction mineral is more likely to
break
- Characterized also by angels cleavage planes form at
- Not everything has cleavage planes
- Generally, there are 3 (like calcite)
- Mica: flat, shiny, sparkly; obvious cleavage as it breaks into thin sheets; across, it has
strong covalent bonds, but different layers have weak hydrogen bonds
- Crystal faces are often mistaken for cleavage planes
- Calcite: rhombonedian cleavage; under microscope it has parallel grains
- If no cleavage planes, will fracture irregularly
Luster:
- Least quantitative, most useful
- Visual texture of something, how it reflects light
- Common lusters: Glassy/vitreous, Metallic (like pyrite), Waxy, Drusy, resinous, Silky,
Pearly (opal)
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Conchoidal fractures: curved lines; ideal: obsidian (rapid cooling of high silica
magma), can tap out cones and break it into ways you want it
Granite:
Quartz: gray, no cleavage, had conchoidal fractures, Hardness 7
 if pure, a grayish-white, clear if one big crystal
 SiO2
 really resistant to destructive environments (will just break into pieces);
physically/chemically durable
 orange is contamination of ion oxide
 lots in sedimentary rocks
 Cryptocrystalline quartz: “secret quartz,” individual grains/crystals are
microscopic; like agate, jasper, and chert (all flint)
 Noncryptocrystalline quartz: primarily classified by color
Feldspar
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Widmanstatten (iron nickel), meteorite rings
Martian meteorites (most are from asteroids)
Mars meteorites form from large asteroids/huge impacts that knock away rocks
parts: heated surface (smooth), and cut off parts
coming in at 10 km/s
Difficult to find: thick layer outside of melted rocks looks exactly like a microbial coating
that forms over rocks that are outside (in desert, called desert varnish)
Iceland Spar: really pretty, clear calcite; has biofringing, where light rays refract  2 images
Examples:
Benitoite: state gemstone, really rare, found in CA and Siberia
Hornblende: trapezoidal cleavage, 56 degree angle
Quartz crystals: at end, called termination, mostly not broken surfaces, but grows with edges
in ideal conditions; if broken, there are no parallel breaks, are conchoidal fractures
Agate: banded cryptocrystalline quartz, commonly reddish brown (hematite), other
contaminants cause color to change
Geodes: agate in which as you go towards the center, there are larger quartz crystals;
the center is hollow
Rose quartz (pink)
Amethyst (purple)
Citrine (Yellow)
Ametrine (Purple)
Aventurine (looks like jade)
Chalcedony (color free cryptocrystalline quartz)