earth science3
ademola
Sep2_Rock_ident.pptx
Combination of minerals rocks
http://www.geology.wisc.edu/~maher/air/air14.htm
Rock Types
Igneous
Sedimentary
Metamorphic
Rock Types - Igneous
Igneous means “formed from fire”
Rocks formed by cooling and crystallization of molten material called magma (or lava)
(remember the two types of magma: basaltic and granitic and their differences)
Granite and basalt look quite different because of a key difference in how they are formed
Granite vs. Basalt
Recall:
Granitic magma is less dense- silica rich.
Granitic magma crystallizes last (remains liquid longer)
Consequence:
Magma that comes out of the ground quickly and becomes lava
is basaltic. Hasn’t had time for the heavy stuff to settle out. Lava cools
very quickly- days/weeks.
Magma that remains underground where the silica rich liquid will separate
out will also cool much more slowly and can take millions of years to finally
get cold enough to crystallize
Analogy: shake up olive oil and water and stick it immediately in the freezer (basalt)
vs. let it for a long time and cool gradually degree by degree so that it freezes
very very slowly (the olive oil is like the granitic magma which will float to the top)
Granite and Basalt look very different
Granite: has time to grow large visible crystals in various random patterns
Granite is often sparkly
Basalt- black volcanic rock.
Crystals are microscopic. Really fast cooling gives you glass (no crystals)
Basalt on the beaches of Oregon
Look at rock samples on webcam…..
Obsidian
(“dragon-glass in Game of Thrones”!)
Some terminology
Crystal: a solid with an organized structure. Atoms have exact
and repetitive spacing, angles etc.
These can be different
atoms depending upon chemical
formula. But it will be in a regularly
repeating pattern
In glass, it cooled so quickly the
the atoms aren’t lined up in any
particular way.
Table salt has a
crystal pattern of
alternating sodium
and chlorine atoms
Can be different atoms, depending
Upon chemical formula, but the
Pattern will be repetitive
Rock Types - Sedimentary
Rock formed from accumulation of weathered* materials (sediments)
may contain fossils;
may show layering;
may have a conglomerate nature with rounded particles or cementation evident;
may contain only one mineral as a result of chemical deposition
Generally dull in appearance (no sparkles!)
* So what’s “weathered” mean??? (future lesson: means “broken up”)
Types of sedimentary rocks- depends upon size of sediments
Mud – smallest particles
Sand- medium sized
Gravel- can look like pebbles glued together
All involved with water sedimentary rock requires
liquid water to form
What does that imply for the Grand Canyon?
Sedimentary rocks-picutures
http://physics.uwstout.edu/geo/gallery
Andrew Alden
sandstone
http://www2.vscc.cc.tn.us/svinson/geo100/sedimentary.html
conglomerate
fossiliferous rock
See webcam for samples…
Rock Types - Metamorphic
Term means “changed from”
Rock formed from pre-existing rocks through the action of high heat (no melting) and pressure
May be very hard and may show crystals but they will be in a linear pattern (foliation) or may show elongation or folding that results from high pressure; certain minerals only form in metamorphic rocks.
Process for making metamorphic rock is like putting clay in a kiln and making pottery
Two types of Metamorphic - 1
Gneiss
Gneiss
Foliated:
flat crystals formed in when sedimentary
rocks are heated and compressed
(a folio is a flat sheet of paper)
slate
Look at webcam
Crystals and foliation:
Crystals will grow perpendicular to the pressure
Flat sheets like with mica (found in
schist)
Two types of Metamorphic - 2
Quartzite
http://www.mii.org/mineral_photos_by_type.htm
http://www2.vscc.cc.tn.us/svinson/geo100/metamorphic.html
Non-foliated (no flat, elongated crystals)
(harder to ID, won’t have to recognize)
(metamorphosed limestone)
Checklist for Identifying Rocks
| Rock type | Visible crystals (sparkles)? | Banded or layered? | Fossils? | Pebbles glued together? |
| Igneous | Yes for granite | No, crystals are random | No, never | No |
| Sedimentary | No- dull in color | Often Flat | Yes | Yes for conglomerates |
| Metamorphic | Yes for foliated | Yes, for foliated but irregular | No, never | No |
Why can’t igneous rock or metamorphic rock have fossils?
Rock Cycle
Rocks can be changed from one type to another through natural geological processes.
The series of processes that comprise these transformations is called the rock cycle.
See Figure 20.37 of text
Deposition of:
Studying the details of the rock cycle
Deposition of:
We next will look at the left side of the cycle. How, where and why rocks are heated,
melted and crystallized. Right hand side (sedimentary rock formation) is
part of water cycle- this will be our 2nd unit starting in a couple of weeks
