Download Metamorphic rocks

3/3/2010
Metamorphic rocks
• The term metamorphic is derived from the Latin term meaning, "change of form".
• These rocks have been altered while in their solid state as a response to the environment. 1
Extreme circumstances of • pressure and • temperature, or • an introduction of certain chemicals,
can cause the existing rocks minerals to recrystallize, and they may even become different minerals all together. 2
1
3/3/2010
Metamorphic rocks
The metamorphics get their name from "meta" (change) and "morph" (form). Any rock can become a metamorphic rock. 3
4
2
3/3/2010
• Metamorphic rocks are rocks that have "morphed"
morphed into another kind of rock.
into another kind of rock
• These rocks were once igneous or sedimentary rocks. 5
How do sedimentary and igneous rocks change?
• The rocks are under tons and tons of pressure, which fosters heat build up, and hi h f t h t b ild
d
this causes them to change. • If you exam metamorphic rock samples closely you'llll discover how flattened
closely, you
discover how flattened some of some of
the grains in the rock are.
6
3
3/3/2010
7
Classification of Metamorphic Rocks
• As with igneous and sedimentary rocks,
metamorphic rocks are classified according to their texture and mineral composition, with texture being the predominant characteristic.
Metamorphic rocks can be subdivided into: hi
k
b
bdi id d i
• Foliated (or layered), and • Nonfoliated (those that are not layered). 8
4
3/3/2010
Foliation
9
Foliated Metamorphic Rocks
Foliation: alignment of mineral from directed stress. stress.
Foliated Metamorphic Rocks:
• Slate
• Schist
• Gneiss
10
5
3/3/2010
Slate
• Slate is a metamorphic rock that is formed when shales and clays are put under great pressure and heated inside the earth for millions of years.
heated inside the earth for millions of years.
• Like shale, it splits apart into sheets, which means that it has good cleavage. • Sl
Slate is usually gray or black
t i
ll
bl k and is used to make di
dt
k
blackboards and roofing tiles. • It is also used to make the table tops for the best pool 11
tables. Slate
12
6
3/3/2010
A small slate sample showing slaty cleavage.
13
The differences between slate and shale.
14
7
3/3/2010
Schist
Schists are usually named by the main mineral from which they are formed. – Bitotite mica schist, – hornblende schist, – garnet mica schist, and – talc schist are some examples of this. Because it has been squeezed harder than slate it is often found folded and crumpled. 15
Schist Rocks
16
8
3/3/2010
Biotite schist
17
Gneiss
These rocks may have been granite which is an igneous rock
granite, which is an igneous rock, but heat and pressure changed it. 18
9
3/3/2010
Gneiss
You can see how the mineral grains in the mineral grains
in the
rock were flattened
through tremendous heat and pressure and are arranged in alternating patterns. 19
GNEISS
20
10
3/3/2010
Nonfoliated texture
Metamorphic rocks with no visible preferred orientation
i t ti of mineral grains have a f i
l
i h
nonfoliated texture. 21
Nonfoliated Metamorphic Rocks
As opposed to the foliated metamorphic rocks, the nonfoliated rocks are not distinctly layered.
22
11
3/3/2010
Nonfoliated Metamorphic Rocks
QUARTZITE
The parent rock for quartzite is quartz‐rich sandstone.
As sandstone becomes deeply buried, rising temperature will fuse the quartz grains together forming the extremely hard and weather‐resistant rock quartzite.
Quartzite comes in many colors, but when pure it is light‐colored.
Quartzite tends to have a sugary appearance.
23
QUARTZITE
24
12
3/3/2010
A comparison of quartzite to quartzsandstone. Note that individual sand grains are readily visible on the surface of the sandstone, but not on the quartzite.
25
Nonfoliated Metamorphic Rocks
MARBLE
• The parent rock for marble is limestone.
As temperature and pressure increase on a body
As temperature and pressure increase on a body of limestone underground, calcite crystals
begin to fuse together and recrystallize.
Marble is an excellent building stone
Marble
is an excellent building stone due to its due to its
uniform texture, softness (calcite is a 3.5 on Mohs hardness scale), and inherent beauty.
26
13
3/3/2010
Marble
• Marble is strong and can be polished to a beautiful luster. • It is widely used for buildings and statues. As you can see from the picture, marble has a very sparkly luster. • Marble can be any color (such as white, pink, gray, red, yellow or black) based on the impurities that may have existed in the original limestone rock.
27
Marble
28
14
3/3/2010
Anthracite
– It forms during mountain building when It f
d i
t i b ildi
h
compaction and friction are extremely high. – This form of coal burns very hot and almost smokeless. – It is used in the production of high grade steel. 29
30
15