Chapter 5, Section 1 Classifying Rocks
I.
How Geologists classify
A. Use texture and chemical composition
II.
Texture – look and feel of the rock
A. Grain size – Coarse-grained or fine-grained
B. Grain shape – from sand through stars to jagged
chunks
C. Grain pattern – flat layers, swirling, rows of
beads, or random
D. No visible grain – some cool so quickly they look
like glass. Others made of extremely small
particles, like flint
I.
Mineral composition
A. Slices thin enough to look through with a
microscope
B. Test with acid or a magnet
II.
Origin
A. Igneous – from cooling of molten rock (magma or
lava)
B. Sedimentary – bit from other places are pressed
and cemented together
C. Metamorphic – existing rock changed by heat,
pressure, or chemical reactions
Chapter 5, Section 2 Igneous Rocks
I.
Characteristics of igneous rock
A. Origin – Ignis means fire
i.
Extrusive rock is from lava (on surface).
Basalt is most common example
ii.
Intrusive rock formed under the surface.
Granite is most common example
B. Texture – size and shape of crystals
i.
Fine-grained from rapid cooling; coarsegrained from slow cooling
ii.
Intrusive rocks have larger crystals
iii.
Porphyritic texture is large crystals in a
background of much smaller crystals – cooling
in 2 stages, like when close to surface
iv.
Basalt crystals too small to be seen
without a microscope
C. Mineral composition – color can change depending
on what is mixed in with rock
II. Uses of igneous rock
A. Tools and building materials
B. Granite monuments are more than 3,500 year old
C. Basalt used in gravel for roads
D. Pumice for cleaning and polishing (soap called
“Lava”)
Chapter 5, Section 3 Sedimentary Rocks
I.
II.
From sediment to rock
A.
Sediment is small, solid particles that come
from rock or living things
B.
Erosion – running water or wind break off and
carry away particles
C.
Deposition – particles are deposited (dropped)
when wind or water slows
i. More sedimentary rock in lakes and deltas
than rivers
ii. Living remains may harden, and then be called
fossils
D.
Compaction – as layers build up, pressure is
created, squishing the particles together. Layers
may remain visible
E.
Cementation – even compacted stuff will fall
apart if there is no glue. Minerals dissolved in
water may seep into the spaces between particles
and crystallize, acting as glue
Clastic rocks
A.
Rock fragments squished together
B.
Shale – from tiny particles of clay, deposited
in very thin layers
C.
Sandstone – from the sand on beaches, etc.
D.
Conglomerate and Breccia – mixture of rock
particles of different sizes. Conglomerate has
rounded edges; breccia has sharp edges.
III.
Organic rocks
A. Coal – from swamp plants buried under water
B. Limestone – from shells made of calcite (coral,
clams, etc.). Some calcite dissolves to form
cement. Chalk is one example
IV.
Chemical rocks
A. When minerals crystallize out of a solution.
B. Some limestone is chemical – stalactites are an
example
C. Rock salt and gypsum are both chemical rocks
formed from evaporation of water
V.
Uses of sedimentary rocks
A. Sandstone and limestone as building materials –
easy to shape but not very durable
B. Limestone for smelting, and in concrete
Chapter 5, Section 4 Rocks from Reefs
I.
Living coral
A. Relatives of jellyfish, who make skeletons that
grow together
B. Only in shallow, warm, saltwater
II. How a coral reef forms
A. Coral change calcium to calcite, to put in skeletons
B. Fringing reefs (close to shore); barrier reefs (at
least 10k out); and atolls (ring shaped island far
from land).
a. Atolls form on top on drowned volcano.
III.
Limestone deposits from coral reefs
A. When coral is buried, the calcite turns into
limestone. Later, uplift exposes the limestone
Chapter 5, Section 5 Metamorphoric Rocks
I.
How they form
A. Heat and pressure can change any rock into
metamorphic rock (including metamorphic rock).
B. Pressure is hundreds or thousands times surface
pressure
II. Classifying metamorphic rocks
A. Use arrangement of grains
B. Foliated (from word for leaf) means arranged in
thin, parallel layers. They split into layers. Slate is
an example.
C. Non-foliated rock has random grains. These do not
split into layers. Marble is an example.
III. Uses of metamorphic rocks
A. Marble for buildings and statutes.
B. Slate for flooring, roofing, and chalkboards.
Chapter 5, Section 6 The Rock Cycle
I.
Many pathways
A. Forces build, destroy, and change the rocks in the
crust.
a. Rock cycle is the processes that change rock
b. Constructive and destructive forces, including
plate tectonics.
II. One pathway
A. Granite batholith formed, then pushed upward by
mountain building forces.
B. Erosion wears away sand particles, and the particles
collect and ultimately form sedimentary rock
(sandstone).
C. As it is pushed downward, heat and pressure start
to build. Eventually the sandstone will
metamorphize into quartzite.
D. The quartzite could be uplifted to the surface, or
melt and return as magma.
III.
The rock cycle and plate tectonics
A. Plate movements drive the rock cycle.
B. Subducting oceanic plates – push igneous or
sedimentary rock down into mantle, where it comes
back to the surface as magma.
C. Colliding continental plates – can power
metamorphic process and provide force for uplift.