Download Rock Identification Lab

Rock
Identification Lab
Purpose: How are different rock types categorized and their origins determined?
Hypo: None! Just observe.
Materials: Rocks
Procedure: Listen to directions…
Data:
Data Table #1: Christman’s Big NW Rock Collection
Sample
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Name
Identifying Characteristics
Type
Sub-type
Rock
Identification Lab
Part II, Questions:
FOR ALL ROCK ANSWERS, WRITE THE ROCK NAME & NUMBER TO IDENTIFY
THE SAMPLE!
Igneous Rocks
The igneous rocks in this collection are numbered 2, 3, 6, 8, 15, 16, 18 & 19. This type
of rock is formed by the cooling of magma either above or below the Earth’s surface. If
the molten material reaches the surface to form a volcano, the erupted rocks are called
extrusive (volcanic). Lava creates this sub-type of rock. The quick solidification of lava
into rock does not allow the molecules time to move into position to form big crystals,
thus the minerals that crystallize are small in size. If the molten material remains
beneath the surface, the rock is said to be intrusive (plutonic). Magma creates this subtype of rock. The insulating effect of the overlying rock allows the magma to solidify
slowly, thus molecules have time to move into a crystal lattice & crystals grow larger.
1. Tell which of the eight igneous rocks are extrusive.
2. Tell which of the eight igneous rocks are intrusive.
3. Which of the extrusive igneous rocks cooled so fast that holes remain where gas
bubbles were trapped in the rock?
4. Which rock probably contained the greatest amount of gas when it solidified?
Describe your evidence for this.
5. As all of these rocks are from Washington State, tell some places where the
intrusive and extrusive rocks might have come from (yes, you can look at a map).
Sedimentary Rocks
The sedimentary rocks in this collection are numbered 1, 5, 9, 11, 13, 20 & 21. All these
sedimentary rocks were deposited in water except the two chemical sedimentary rocks
that were left over after the water evaporated. The amount of motion (kinetic energy) of
the water determines what size particles of sediment can be carried and what kind of
sediment will be deposited when the motion decreases. The faster the water moves, the
larger the size of the rocks/sediments that can be carried. With the slowing down of the
water, the largest rocks/sediments will be deposited first, and the finest material will be
deposited last. Limestone forms in quiet water by the slow accumulation of calcite from
shells of living organisms. Coal forms by the accumulation of the organic remains of
trees and other plants in swamps or still water. The carbonaceous material is converted
to coal by the pressure of being buried and/or folded.
6. Tell which sedimentary rock (only 1 for this Q) had sediments that were deposited by
fast moving water.
7. Which sedimentary rocks (3) had sediments that were deposited in quiet water?
Rock
Identification Lab
8. What kind of place do you think the sand that became the sandstone (rock #9) was
deposited? What sub-type of sedimentary rock would sandstone be?
9. Which 2 rocks were the result of dissolved minerals forming a rock after the water
evaporated away?
10. Tell the sample #s & names of the two sedimentary organic rocks.
11. Look at all 18 rock samples. Which specimens are rounded, suggesting they were
transported or carried by water prior to being collected? That is, which specimens do
you think were collected along a river or beach?
Metamorphic Rocks
The metamorphic rocks in this collection are numbered 4, 7, 10, 12, 14, & 17. Originally
each of these rocks was some kind of igneous or sedimentary rock before it was
metamorphosed (changed) by heat and pressure. New minerals form by recrystallization but the overall composition of the rock usually remains the same. If the original
rock contains only CaCO3 (calcium carbonate) the resulting metamorphic rock can
contain only CaCO3, although the texture may change through recrystallization. Usually,
with high temperatures the sizes of the crystals become larger. Thus, a fine-grained
rock can be metamorphosed into a coarse-grained rock. However, a rock that originally
is coarse-grained does not become coarse-grained from metamorphism.
Side-note: anthracite is a borderline case. It was formed from calcium carbonate
sediments that underwent heat and pressure and thus could be considered a
metamorphic rock. However, in this lab it is considered to be a sedimentary rock
because the sedimentary rocks above and below it show no evidence of
metamorphism. This indicates that the heat and pressure must have been relatively low.
12. Tell which metamorphic rock was limestone before it was metamorphosed.
13. Tell which metamorphic rock was a quartz sandstone before it was metamorphosed.
14. Look at the specimen of basalt (#2). If it were metamorphosed only slightly (lowgrade heat & pressure), which one of these six metamorphic rocks would form by
recrystallization?
15. Shale consists primarily of clay minerals, which are easily metamorphosed into a
variety of different rocks by metamorphism. Tell the three remaining metamorphic
rocks that were probably shale originally. (Name rocks that are different from those
used for answering questions 12, 13, & 14)
16. Of your three answers to question #15, which rock most likely formed under lowgrade heat and pressure conditions of metamorphism?
17. Specimen #17 was difficult to identify as being a metamorphic rock. What clue was
helpful in identifying the rock as metamorphic?