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Hard as a Rock

More STEM Resources at http://earth.appstate.edu/outreach

Teacher Instructions

ELABORATION: “DON’T TAKE IT FOR GRANITE”

To go deeper into properties of rocks, the teacher can demonstrate rocks that are smelly (sulphide-containing rocks rubbed on a streak plate or pieces of flint rubbed together), rocks that are attracted to magnets because of their iron content (magnetite and hematite), UV glowing rocks (eg. rocks with calcite, fluorite or celestite), rocks with very low density that float in water (pumice) or those that reach with acid (limestone).
Rock density is an important factor in determining uses for rocks. Higher level students can explore rock density by trying the activity called “Don’t Take it for Granite!” in which they try to show that a sample of countertop is sandstone and not granite by its density. When setting up this activity:

Each group of students gets two sampled labeled A and B. A should be a granite, B should be a sandstone.
This is a more advanced, open-inquiry activity. To provide students with more guidance than is provided in the handout, you can:

Demonstrate how to use Archimedes’ principle to measure volume of an uneven object using a measuring cylinder to find water displaced when the object is placed in it.
Provide the mass for sample A and sample B.
Provide densities of the rocks.
Do the activity as a class

For more information on how to use the Claims, Evidence, Reasoning framework for writing scientific explanations, visit:

https://youtu.be/5KKsLuRPsvU (Video)

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Hard as a Rock

More STEM Resources at http://earth.appstate.edu/outreach

Name:

Don’t Take it For Granite! Activity

Your family is looking into building a cool picnic table in your backyard. They want to build it out of rock so it lasts longer, so they request granite samples from a nearby construction materials store and are sent a couple back.

You really like the brownish sample “B” because it has neat patterns in different shades, but from your science lessons, you are convinced it’s not a a granite but a sandstone. Your family doesn’t quite believe you, the store said they are both granite and are both priced pretty highly as such. You remind them you got an A- in the rock science unit and will proof to them that “B” is indeed sandstone.

GRANITE

Things that might identify a sample as granite:

Density listed online: _______

SANDSTONE

Things that might identify a sample as sandstone:

Density listed online: _______

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The Question/ Problem:
Your claim:
Your evidence: Density= mass ÷ volume Mass of (A)= _____g Volume of (A)= _____ cm3 Density of (A)= ______ g/cm3 Mass of (B)= _____g Volume of (B)= _____ cm3 Density of (B)= ______ g/cm3 Other evidence from your observations:	Your reasoning:

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Students learn that rocks have different densities and that their density often determines their use. They compare different rocks densities and write their observations using the C-E-R framework.

Demo: Find samples of granite and pumice that are similar in same size. Pass them around the classroom and have students share which one feels heavier. As discussion prompts, you can ask “In what ways do the two samples look and feel different?” “Which one would you use to build a prison? Why” “Why IS granite heavier than pumice?”

Explain that “There are many more particles of granite stuffed into the same space than there are of pumice. This is called density. Rocks that are dense feel heavier. We don’t use weight to compare rocks, since it varies depending on the size of the rock, we use density, which measures how much stuff is packed into each rock. Density is always the same for a specific rock, so whether you are looking at a granite sample the size of a house or one like the one we have, it will always have a density of 2.69g/cm3 (Find a wooden cm3 block of something similar to illustrate this size).”
This can also be illustrated using two identical bowls: one filled with marshmallows and one filled with metal coins. They take up the same space but coins one is heavier because metal has more density.

On the board write:

Granite- 2.69g/cmЗ

Pumice- 0.64g/cm3

Gold- 19.32 g/cm3

This is a great opportunity to bring in the story of Archimedes and the bathtub! Here are some useful resources:

Archimedes video: https://www.youtube.com/watch?v=AyFwhY2413Q

Abbreviated cartoon: https://www.quora.com/What-exactly-was-the-discovery-by-Archimedes-in-the-incident-when-he-later-yelled-Eureka-in-the-street

Archimedes longer cartoon and lesson plan ideas: https://serpmedia.org/scigen/m2.1.html

Hard as a Rock

More STEM Resources at http://earth.appstate.edu/outreach

Teacher Instructions