Rocks
Objectives:
1. How do the three main types of rock form?
2. 2. How are the three main types of rock classified by scientists?
IGNEOUS ROCK
Formation:
(fig. 5, pg.78)
MAGMA
LAVA
when liquid rock cools and hardens
Some igneous rocks form INSIDE the Earth,
and some form ON TOP OF the Earth.
is liquid rock INSIDE the Earth.
is liquid rock which flows ONTO the surface of
the Earth.
Classification:
First by CHEMICAL COMPOSITION and then by
TEXTURE:
CHEMICAL COMPOSITION
Granite Family
light colored; has the most quartz. (fig. 2, pg.
75)
Diorite Family
medium colored; has almost equal amounts of
quartz to iron containing minerals.
Basalt Family
dark colored; has the least amount of quartz;
has the most iron containing minerals.
TEXTURE
COARSE textured
FINE textured
Exceptions
EACH FAMILY is next classified by texture. (fig.
3, pg.76)
igneous rocks
- have large visible grains
- cool SLOWLY underground = INTRUSIVE
Examples are: Granite, Diorite, and Gabbro
igneous rocks
- have small, barely visible grains
- cool RAPIDLY on the surface = EXTRUSIVE
Examples are: Rhyolite, Andesite, and Basalt
Porphyry (fig. 6, pg.79)
- cools slowly underground
- then moves toward the surface and cools
quickly
- so BOTH coarse and fine texture are present
Some igneous rocks have NO TEXTURE
because…
- they cool too quickly to form crystals
Example is Obsidian.
-
thick, bubbling lava cools with many holes,
and without crystals
Example is Pumice.
SEDIMENTARY Rocks
Formation:
(fig. 9, pg.83)
By CEMENTATION, which is the process of
sediments (small pieces of rock) getting coated
with natural cements, and then binding together.
Classification:
Into 3 Main Types:
CLASTIC
Sedimentary Rocks (fig.10, pg.84)
- Are fragments of rocks and minerals that get
deposited usually by water or wind, then
cement together.
- Are grouped by the size of the sediments.
- the smallest are CLAYS
-an example is Shale
- the medium are SANDS
-an example is Sandstone
- the largest are PEBBLES
-an example is Conglomerate
CHEMICAL
-
ORGANIC
Sedimentary Rocks (fig. 13, pg.86)
- Form from minerals once dissolved in water.
- Are formed by one of the following processes:
-evaporation then cementation, these
are called EVAPORITES, an example
is Halite
-precipitation then cementation, these
are called PRECIPITATES, and
example is Chert
Sedimentary Rock (fig.18, pgs. 90 & 91)
- Form from the remains of animals (shells,
bones) cemented together, an example is
Coquina.
- Form from decayed plant material over millions
of years, and example is Coal.
METAMORPHIC ROCK
Formation:
Classification:
There are 2 Types:
1. FOLIATED
2. UNFOLIATED
Intense heat and pressure of an existing
Igneous, Sedimentary, or even another
Metamorphic rock can actually change
the texture and mineral content of the
rock into a new rock.
Examples are:
- sandstone to quartzite
- shale to slate
- slate to phyllite to schist
- schist to gneiss
which contain obvious layers
An example is Gneiss.
which is without obvious layers
An example is Marble. (fig. 19,
pg.92)