Unit 2: Physical Geology-Minerals and Rocks
ES Standards 3.6-Describe the rock cycle and processes responsible for igneous, sedimentary, and
metamorphic rocks. Compare the physical properties of these rock types.
SIS Standards: 1, 3, 4
Common Rocks Lab
Purpose:

To determine if a rock is igneous, sedimentary, or metamorphic by using
identification keys to identify unknown rocks.
Materials:
rocks
magnifying lens
Glass plate
copper penny
HCl
streak plate
Procedures:
(1). Obtain a box of unknown rocks along with supplies to use for this lab. Make sure to keep the rocks in
the numbered slot in the box. #’s_________ are Igneous rocks. #’s _________ are Sedimentary
Rocks. #’s __________ are Metamorphic rocks.
(2). Using the igneous rocks, determine their texture (size, shape of crystals). Coarse-Grained
(phaneritic) have large, uniform sized crystals seen without a microscope/lens. Fine-Grained (aphaneritic)
have very small crystals for which a microscope/lens is needed. Porphyritic have two very contrasting
sizes of crystals. Glassy lacks crystals. Fragmental has broken, angular fragments of rocky material.
Record info in table.
(3) Using the same igneous rocks, determine composition. Felsic (granitic) is composed mainly of lightcolored minerals quartz and potassium feldspars. Dark-colored minerals are less than 15% of the rock.
Intermediate (andesitic) has a mixture of light-colored and dark-colored minerals. Dark minerals comprise
15% to 45% of the rock. Mafic (basaltic) have dark-colored minerals such as pyroxene and olivine that
account for over 45% of the rock. Ultramafic is almost entirely composed up of dark-colored minerals
pyroxene and olivine. Record info in table.
(4). Obtain a classification key for Igneous rocks and identify the Igneous Rocks in your sample box.
Sketch a diagram showing the arrangement of mineral crystals in an igneous rock that was coarsegrained.
(5). Using the sedimentary rocks, determine type of sedimentary rock. Detrital rocks are made of
pieces or fragments of mineral and/or rock material. Chemical rocks are made up of shells or shell
fragments and crystals. Record info in table.
(6). Using the same sedimentary rocks, determine texture and composition. Coarse has large grains,
Medium feels ‘sandy’, Fine has grains 1/16 of a mm and Very Fine has grains 1/256 of a mm. Are the
grains round or angular? Are they made up of quartz, clay or mixture? For chemical sedimentary rocks,
does the rock effervesce (fizz) when HCl is added to it directly or to the streak? Record info in table.
(7). Obtain a classification key for Sedimentary rocks and identify the Sedimentary rocks in your box.
Sketch a diagram of a coarse detrital rock.
(8). Using the metamorphic rocks, determine texture. Foliated rocks have crystals that are elongated or
arranged in parallel layers/sheets. Banded foliated rocks look like they have bands of segregated crystals.
Nonfoliated rocks do not have layers/bands of crystals. Record info in table.
(9). Using the same metamorphic rocks, determine grain size. Foliated rocks have grains that can be
Very fine (not visible), Fine (barely visible), Medium to coarse (visible), or Banded (segregated with
medium to coarse grains). Nonfoliated rocks have Crystalline (fine to coarse) grains, Fused quartz grains
(fine to coarse) and Fine grains.
Analysis:
1. Briefly describe how igneous, sedimentary, and metamorphic rocks are formed.
2. All three types of rocks contain crystals. What unique factor about the arrangement of mineral crystals
occurs in many metamorphic rocks?
3. How would you describe the difference between a detrtial sedimentary rock and a chemical
sedimentary rock to an elementary school aged student?
4. Of the three types of rocks, which one is most like to contain fossils and explain your reasoning for your
choice.
5. Explain what determines the size of crystals in igneous rocks.
Summary: Rocks form from a variety of processes and one rock type can be changed into another.
Explain this cycle and how these rocks can be used to help one understand Earth’s history.