Download Classifiying Sedimentary Rocks

Classifiying Sedimentary Rocks
NAME ____________________________
Sedimentary rocks may be classified into three groups based on what they are made of and how they were formed. If the sediments
that make up the rocks came mostly from the shells of animals or from the body parts of plants and animals, the rocks would be
classified as organic sedimentary rocks. If the sediments were produced from elements that were dissolved in water but later came
out of solution, the rocks would be classified as chemical sedimentary rocks. When elements come out of solution, the elements
are said to have precipitated and the process is called chemical precipitation. Chemical sedimentary rocks are also called
evaporates. If the sediments were formed from particles that were weathered from other rocks, the rocks are called clastic
sedimentary rocks. Clastic sedimentary rocks are classified on the basis of the size of the sediment particles that the rock is made
of.
The chart of common sedimentary rocks summarizes the characteristics of the primary types of sedimentary rocks.
Sedimentary rock type
Particle size or
composition
Rock name
Organic sedimentary rock
If the rock is made up of mostly
shells
If the rock is made up mostly of plant
and animal remains
Limestone
Formed from the remains of living things
such as plants and animals
Chemical sedimentary rocks
Formed when elements that were
dissolved in water come out of solution
Coal
(bituminous)
Sediment particles are too small to be
seen with the unaided eye.
If the mineral material that comes our of
solution is
Calcite then the rock is ---------Dolomite then the rock is -----Halite then the rock is----------Gypsum then the rock is ------
Limestone
Dolomite
Rock salt
Gypsum
Clastic sedimentary rock
Name and size of Particles
Boulder –sized
Conglomerate
Cobble -sized
Conglomerate
Pebble- sized
Conglomerate
Sand-Sized
Sandstone
Clay sized
Shale
Refer to the chart to complete the table below and answer the questions on the next page.
Formed when the particles that are
weathered from other rocks are
cemented together to form a new rock.
(also called fragmental rocks)
Fill in the sedimentary rock types and sedimentary rocks described in the following table.
Description
1. The sedimentary particles are formed by
chemical precipitation and are too small to
see with an unaided eye.
2. The sediment particles are mixtures of sizes
that range between 3.0 and 20.mm
3. The sediment particles are pieces of shells.
4. The sediment particles are sand- sized.
5. The sediment particles are parts of plants
and animals
Sedimentary Rock Type
Rock Name
1. What sedimentary rock can be formed in two different ways?
2. Describe the two ways that this rock can form.
3. What is the only sedimentary rock type that can be formed from things that were once alive?
4. Table salt used to season foods is made of the mineral halite. What sedimentary rock is also made of halite?
Classifying common igneous rocks
For a rock to be classified as igneous, it must have been melted at some time and then hardened to become solid again. When
melted rock material cools and hardens, it may form crystals, depending on how fast it cools. How fast the rock material cools
depends on where it cools. If melted rock cools deep within the earth, the resulting rocks are referred to as intrusive igneous rocks.
They cool very slowly , giving crystals long periods of time to grow. The more slowly they cool, the larger the crystals are. Intrusive
rocks have crystal sizes, or grain sizes, that are larger than sand- sized and, under rare circumstances, may be larger than a penny.
If the melted rock materials cooled near or even on the earth’s surface, the resulting rocks are called extrusive igneous rocks.
However, some extrusive igneous rocks cool so fast that crystals don’t have sufficient time to grow at all.
Sometimes when extrusive igneous rocks are cooling, volcanic gases bubble through the melted rock material much like water
vapor bubbles through boiling water. When the rock hardens, these bubbles may become trapped to produce holes in the final
product. The holes tend to make the rock light in weight.
Mafic
(Iron and magnesium)
High
Dark colored or green
Density
Color
Gabbro
Larger than
sand- sized
Coarse
Composition
Rhyolite
Basalt
Obsidian


than sandsize
Fine smaller
Crystal Size
INTRUSIVE
Felsic
(Aluminum)
Low
Light colored
or red
Granite
Extrusive
 No crystals
 The material cooled to quickly to
allow time for crystals to form

Pumice



Scoria


Commonly called natural or volcanic glass
Most commonly black but may be red, gray or
brown
Breaks in conchoidal or shell-like fractures
Very porous volcanic glass
Color from white to yellowish gray to gray brown
Made of silky glass fibers full of tiny pores. Millions
of pores make pumice so light that some floats in
water.
Color from reddish brown to dark gray to black
Has many holes but they are larger and wider
spaced than in pumice
Refer to the chart to answer the following questions and complete the table on the next page
Igneous rocks may be classified on the basis of color and crystal size. Name the igneous rocks whose crystal size and color are
listed in the following table.
Crystal size
Large
Color
Generally pink
Large
black
Smaller than sand- sized
Blackish green
Smaller than sand-sized
Generally light colored
1.
Rock Name
List two intrusive igneous rocks.
2. Did these two types of igneous rocks cool relatively fast or slowly? Explain your answer.
3. Do all extrusive igneous rocks contain crystals? Explain your answer.
4. Why do some igneous rocks have bubble holes?
5. List two extrusive igneous rocks that contain crystals.
6. Granite and obsidian are similar chemically. How are they different?
7. What igneous rock may have cooled deep beneath the earth’s surface and have a dark blackish-greenish color?
8. Igneous rocks can be classified and mafic or felsic depending on the amount of aluminum or iron and magnesium they
contain. What are two igneous rocks that are felsic and are light in color?
9. Which of the two rocks you listed contains the largest crystals?
10. Name one mafic igneous rock formed when melted rock material cooled near the surface of the earth.
11. Is the rock you listed classified as having a high density or a low density?
Classifying Metamorphic Rocks
In the classification of rocks, a petrographer usually uses what is called a field classification. Field classification represents a broad
framework into which the majority of rocks can be placed. It is based primarily on the texture of the rock and upon its mineral
composition. These are the two main characteristics of a rock that one should look for in a specimen. Metamorphic rocks are
“changed rocks”. That is that they have been altered from some other sedimentary, igneous, or other type of metamorphic rock.
They may still possess some of the characteristics of the rocks from which they were made. As a result, it is easy to make a mistake
in the rock’s classification. Because metamorphic rocks have been changed, they are usually very hard. Heat, pressure, and
chemical alteration affect they way the rock looks. They, hardness is the third most important factor in classifying a metamorphic
rock.
Texture
The differences in the orientation, or alignment, of the crystals and the size of the crystals determine the texture of the metamorphic
rock. There are two general texture groups. Foliated textures are those in which platy or leaf-like minerals such as mica or chlorite
are nearly all aligned parallel to one another. As a result, the rock splits readily along the well- oriented, nearly parallel cleavages of
its mineral particles.Non foliated textures are composed of either randomly oriented or platy minerals or minerals that are not
foliated. Metamorphic rocks that are nonfoliated will break into angular pieces. Many times metamorphic rocks that are
nonfoliated are classed massive. Marble and quartzite are the best examples.
There are 5 basic textures found in metamorphic rocks
Gneissose
Schistose
Coarsely foliated with coarse mineral grains
Finely foliated with thin parallel bands along which the rock splits easily
Slaty
Very fine foliated producing almost rigidly parallel planes of easy splitting.
Granoblastic
Unfoliated or only faintly foliated
Hornfelsic
Un foliated with mineral grains that are commonly microscopic: breaks sharply into angular pieces
Simplified identification table for metamorphic rocks. Study it carefully and answer the questions.
Unfoliated or Lightly Foliated Metamorphic Rocks
Metamorphic rock
Texture
Commonly derived from
Hornfels
Quartzite
Marble
Amphibole
granulite
Hornfelsic
Granoblastic, fine grained
Granoblastic
Granoblastic
Granoblastic
Any fine-grained rock
sandstone
Limestone, Dolomite
Basalt, Gabbro, Tuff
Shale, igneous rocks
Foliated Metamorphic Rocks
Metamorphic rock
Slate or Phyllite
Schist
Chlorite
Mica
amphibole
Gneiss
Texture
Slaty
Schistose
Commonly derived from
Shale, tuff
Basalt, Andesite, Tuff
Shale,Rhyolite, Tuff
Basalt, Andesite, Gabbro
Gneissose
Granite, Shale, Diorite, Mick schist,
Rhyolite
Migmatite
Coarsly banded, highly variable
Mixtures of igneous and other
metamorphic rocks
1. The classification of rocks is based primarily on ___________________ and _________________________
composition.
2. Name 5 basic textures of metamorphic rocks
a.
b.
c.
d.
3. Name the five most common types of metamorphic rocks.
a.
b.
c.
d.
4. Name the metamorphic equivalent of the following.
a. Limestoneb. Sandstone –
c. Granited. Shale 5. For each of the following descriptions, indicate the type of metamorphic rock.
a. Granoblastic, fine to coarse-grained, composted mainly of calcite, dolomite or both.
b. Very fine-grained, exceptionally well-foliated rock.
c.
Coarse-grained rock with distinct layers or lenses of different minerals: among the most plentiful of metamorphic
rocks
d. Very hard, sugary-textured granoblastic rock: very widely distributed: made of interlocking quartz grains.
e. Hard, unfoliated, very fine-grained rock that breaks into sharp angular pieces