Transcript Rocks - Klahowya Secondary School

Rocks
Chapter 4
Classifying Rocks
Mineral Composition - Look with a
magnifying glass to determine the
mineral that makes up the rock
 Color - Light or dark color, glassy?
 Texture – look and feel of the rocks
surface
 Grain size – Fine, coarse or no visible
grain
 Grain Shape – Rounded or jagged
 Grain Pattern – non-banded, banded

Rocks
is a rock?
 mixture of minerals, mineraloids, glass
or organic matter
 3 Types of Rocks:
 1. Igneus Rock – molten material
inside earth or from a volcano cools
slowly due to the insulation of rock
allowing the atoms to arrange
themselves into large crystals called
mineral grains
 What
 Remember:
magma forms from
great temperatures
(1400oC) and
pressure in the
earth this melts the
minerals and forms
magma
 When magma flows
to the surface it is
called lava
Intrusive Rocks
Intrusive Rocks– formed when
magma insulated and trapped
below the earth surface, holds
heat and cools slowly – large
mineral grains
 Granitic – light colored rocks,
lower density contains a lot of
silicon and oxygen, mountains
Extrusive Rocks
 Extrusive
Rocks – Formed when
magma cools on the earths surface
and cools rapidly –
fine grained texture Basaltic –
dense, heavy, dark colored (magma)
examples iron, magnesium, covers
ocean floor
Combination:
Andresitic – in between basaltic and
granitic in mineral composition
Igneous Rocks - Texture
 Intrusive—Large
crystals
 Extrusive—Small Crystals (maybe
not visible: obsidian & Pumice)
 Mafic—Dark
 Felsic—Light
Obsidian
Pumice
Andesite
Rhyolite
Diorite-Dark color w/ large black
crystals
Basalt
Gabbro
Granite
Sedimentary Rock

Sedimentary rock -comprises 75 % rocks on
earth -formed when sediments pressed or
cemented together – may form layers
 Sediments – loose materials such as rock
fragments, grains and bits of plant and
animals
 Compactation – pressure causes sediments
to form rock
 Cementation – water dissolves minerals
(quartz, calcite, hematite, limonite) natural
cements

Classification of sedimentary
rock:
 Clastic – broken, named for size &
shape of sediments example –
conglomerate, breccia, sandstone,
shale
 Chemical – minerals precipitated
from a solution or evaporates
example – limestone, rock salt
 Organic – from once living things
examples – coal, chalk
Sedimentary Rocks


Compacted or Cemented (layering is key)
 Sandstone
 Shale
 Coal (rock or not? Some debate)
Clastic
 Breccia—sharp angles
 Conglomerate—rounded edges
(concrete)
 Coquina—Shells
Coal
Sandstone
Mudstone-gray & silky soft
Shale
Conglomerate
Breccia
Coquina
Coral Reefs
Formed from skeletons of tiny coral animals
that grow together to form the coral reef
structure
 Almost all coral reef growth occurs within
the top 40 meters of the surface where
sunlight penetrates
 Coral organisms need warm water, found
only in tropical oceans
 Limestone deposits formed from coral reefs

Metamorphic Rock


Metamorphic rock – rocks changed due to
temperature and pressure increases or
change in composition
Classification of Metamorphic Rock



Foliated – mineral grains flatten and line up in
parallel bands Example slate and gneiss
Slate forms from shale which is arranged in
layers when exposed to heat and pressure
Nonfoliated – no banding occurs, the mineral
grains change, grow and rearrange but no bands
Example is marble which forms from sedimentary
rock calcite – shiny. Hornblende and serpentine
– green.
Hermatite - red
Metamorphic Rocks
 Gneiss—Zebra
strips
 Schist—Metallic shine
 Marble—Contains Calcite (bubbles
w/HCl)
 Or Morphed sedimentary rock
 Slate (shale that has hardened)
Gneiss
Slate
Schist
Marble
Phyllite
Rock Cycle