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Rocks and Minerals Review Guide

1.      Identify each of these as sedimentary, metamorphic or igneous.  Explain you reasoning.

The one on the left is sedimentary (probably conglomerate), you can tell that those pieces inside are rounded and must have been weathered before being cemented together.

The middle one is metamorphic, you can tell because of the wavey foliations (a sedimentary rock might have layers, but they’d be flat).

The one on the right is igneous.  It has large crystals which means it probably formed deep within the earth (intrusive).

2.      List the order in which these geologic features formed.

Most recent:

A

B

C

D

F

E

G

J

H

I

Oldest

3.      Which diagram represents a landscape where fine-grained igneous bedrock is most likely to be found?

 

4.      Describe how the rate of cooling effects the texture of a rock.

The faster a rock cools the smaller the crystals (or the finer the texture of the rock).

 

5.      Describe how igneous rocks are formed.

Igneous rocks are formed from magma that cools and solidifies.

 

 

6.      What kind of rocks are formed as a result of heat and pressure beneath the Earth’s surface?

Metamorphic rocks are formed as a result of heat and pressure beneath the Earth’s surface.

7.      What kind/s of rock can contain fossils?

Sedimentary are the only rock type that can contain fossils.

8.      What kind/s of rock are made from magma?

Igneous rocks are made from magma.

9.      Which of the following happen most quickly?

a.      subduction                          b.  folding                                 c.  faulting

10.   Explain the difference between absolute age and relative age in terms of how we determine each and what each tell us about the rock.

Absolute age is the actual age of the rock.  We use radioactive istopes to help us figure out the absolute age.  We can only determine the absolute age of igneous rock and fossils.

 

Relative age tells us how old the rock is in comparison to surrounding rocks and geologic features.  It doesn’t give us a number, it only allows us to rank things.

 

 

 

 

 

 

 

11.   What is happening at Valley X that is not happening at Valleys Y or Z?

 

Faulting is happening at Valley X.

12.   A rock that originally contained 400 grams of Uranium-235 now contains 25 grams of Uranium-235.  How many half lives have passed since this rock was formed?

400g à 200g à 100g à 50g à 25g

Each arrow represents one half life.  Four half lives have passed since this rock was formed.

13.   Uranium-235 decays through a long but relatively fast series into Lead-206 which is stable.  In the following diagrams, the black dots represent U-235 atoms and the white dots represent Pb-206 atoms.  According the principle of radioisotope dating, which of the following rocks is the youngest? oldest?

 

 

 

 

 

 


                                                                                                                              Youngest                              Oldest

14.   A sample of an unknown mineral has a mass of 145g and a volume of 53.7 mL.  What is the density of this mineral?  What mineral is it?

 

D = m/v

D = 145g/53.7mL

D = 2.7g/mL

This sample is quartz

15.   What causes minerals to have different crystal shapes?

The arrangement of atoms inside the crystal is what causes minerals to have characteristic shapes.

16.   Where will you usually find the youngest sedimentary rock in a rock outcropping?

The youngest sedimentary rock is usually found at the top of a rock outcropping.

17.   Conglomerate is a fragmental sedimentary rock (it is composed of small rocks cemented together by fine particles).  How might this type of rock form?

Conglomerate might be formed in an old river bed that has small rounded pebbles surrounded by small sand and silt grains.  If this river bed is burried and exposed to enough pressure the rounded pebbles will be cemented together by the sand and silt grains (as well as other cementing agents).  The rock that results is called conglomerate.

18.   Where do intrusive igneous rocks form?  Where do extrusive igneous rocks form?

Intrustive igneous rocks form deep within the Earth.  Extrusive igneous rocks form at the Earth’s surface.

 

19.   How might you be able to tell the difference between an intrusive and extrusive igneous rock?

Intrustive igneous rocks will tend to have larger crystals (coarse texture).  Extrusive igneous rocks will tend to have small (invisible to the naked eye) crystals.

 

20.   What processes change a sedimentary rock into sediments?

Weathering and erosion change sedimentary rock into sediments.

 

21.   What does it mean to say that a rock is foliated?

A foliated rock has visible layers (may or may not be flat).

22.   Identify three different ways a sedimentary rock can form.

Sediments forming as water evaporates away.

Sediments becoming pressed or cemented together.

Organic material becoming pressed or cemented together.

 

 

 

 

 

 

23.   What kind of substance (discussed in this unit) is made of either an element or a compound, but never a mixture?

Minerals are composed of an element or a compound.

24.   List at least 4 different characteristics used to identify minerals and briefly explain each.

Hardness – tested by doing scratch tests.

Density – mass/volume

Crystal Structure:  observing the shape of the crystal

Streak – observing the color the mineral leaves on a porcelain streak plate

Magnetism – observe whether or not a mineral is magnetic

Fluorescence – observe whether or not a mineral fluoresces when exposed to UV light.

 

 

 

 

 

 

25.   Which of the following sedimentary rocks is the oldest?  youngest?

The black shale in outcrop B is the oldest and the tan siltstone in outcrop A is the youngest.

 

26.   In outcrop C, which happened most recently, faulting (at X-Y), an igneous intrusion, contact metamorphism or an unconformity?

The faulting happened most recently.

 

27.   What rock type accounts for the vast majority of the rocks shown in these outcroppings?

Most of these rocks are sedimentary.

 

28.   Why is the volcanic ash layer considered a good time marker for correlating rocks?  The volcanic ash was deposited at the same time over a large area.

29.   What name is applied to coarse grained, mafic rock?

Gabbro (peridotite or dunite would be ok too).

 

30.   What are the three most common minerals found in andesite?

 

Plagioclase feldspar, biotite and amphibole are the most common minerals in andesite.

31.   How does dolostone form?

Dolostone forms as a result of evaporation of water.  The minerals in dolostone are left behind.

 

 

32.   What clastic rock has the largest grains of sediment?

Conglomerate

 

 

33.   What sedimentary rock is primarily made from the mineral halite?

Rock Salt

 

 

34.   What kind of rock sedimentary rock can change into quartzite?

Quartz sandstone.

 

 

35.   Which foliated metamorphic rock has the largest crystals?

Gneiss

 

36.   List the labeled rocks in order of decreasing age.

Schist, Granite and Shale

 

 

37.   What is the line from A to A’ evidence of?

An unconformity:  a period of time where the rocks were exposed, erosion occurred and rocks were transported away.

38.   Did the tilting of layers 5 and 6 happen before or after the intrusion labeled 7?

Before.

 

39.   Use the rock type tables to help you figure out what kind of rock probably formed as a result of contact metamorphosis of layers 5 and 6.

 

layer 5 (limestone) probably became marble.

layer 6 (shale) probably became slate.