How to Make a Rock - a Primer Into Earth Science

Introduction:

Hello!  I have been a long time lurker on Instructables.  Everyday I see fantastic Instructables and that I would love to do in my classroom.  Many of them I do for pure enjoyment on my own free time but I scour daily for ones that my students can actively create/participate.  I believe that being able to follow instructions and create something on their own is a valuable skill to nurture; having them take it a step further to add their own spice just makes me a proud teacher.  Typically my students see earth science as the boring part of the year and this introduction grabs their attention by giving them the challenge to make a rock which they may also get to keep. 

This Instructable is something that all students should be able to do, the usual problems of lack of time, relation to STEM education standards and level of difficulty/safety is not an issue here.  So to all the teachers(and anyone else) here is a quick, easy and cheap way to introduce Earth Science.  I have done this with mostly elementary students but can be scaled up to middle school depending on your needs.

Learning Objectives

a.  Observe and describe rocks by size, texture, and color
b.  Explore the processes that lead to the formation of different rocks
c.  Observe and identify changes to Earth's surface caused by natural occurrences such as weathering and erosion.
d.  Test the physical properties of minerals including hardness, color, luster, and streak.

*** There are more but they all fall into the observe, make inference type of all purpose standards or loosely touches upon physical science standards.

Step 1: Step 1 - Gather Materials

What you need:

- Aluminum foil of any variety, cost or brand
- A smooth surface e.g. a table or desk

That's it.

Just a warning though, due to the nature of this lab the table will end up with some streaks and markings.  Be prepared and do a small test rub first and see if it washes off your surface before going full scale. 

One roll of aluminum foil should last for several classes, assuming 25ish students.

Step 2: Step 2 - Getting Started

1.  Rip off a piece of aluminum foil of any size.  The shape, straightness or even side of the foil do not matter.  I would recommend to start off with a 10" x 12" or similar size piece which produced the larger rock from the introduction picture.

2.  Crumble it into a ball, try your best to compact it as much as possible with your hands while still keeping a ball-like shape.  Do not flatten it or form sharp angles typically found in geometric shapes. 

Step 3: Polish!

The next few steps are where you either make a rock or a piece of foil mess.  Thankfully foil is cheap so if something does go airy, no worries. 

1.  Hold your crumpled piece of foil and firmly(but not to hard!) rub it against a smooth flat surface.  I used a lab table.

2.  Don't over do it! 

3.  Stop and examine the part that was rubbed and you can already see a nice shiny flat surface forming and the folds of the foil starting to compress and smooth out. 

4.  Slightly turn the rock and continue rubbing the foil piece against the table.  Make sure to frequently check that you are not putting to much pressure and causing the rock to become overly flat. 

5.  Now examine the 2 areas you have started to smoothed out, you should have created a edge between the 2 smooth surfaces.  We need to also get rid of this, so turn the rock so the edge faces the table and also try to round out that edge.  Remember the goal is to make the rock as round as possible. 

6.  Repeat steps 1-5 until all of your rock has a fairly decent polish and coming to shape.

Teachers note:

While the students are doing this, walk around and encourage the observation part of this lab.  See if the students can recall about friction since the rock should be getting warm.  But also talk about pressure/heat in a metamorphic rock creation, and equally important ask the students about the little fragments of foil that flaked off and the streaks on the table.  What would they form if they are allowed to stack for many years?  Also to note, the size of the ball should be dramatically decreasing, explanations and such should be documented in their journals. 

Step 4: Fork in the Road

Fork in the Road:

Now at this point we got a semi-finished rock.  There should still be quite a few rough edges, maybe some gaps that I call crevices and accidents of either over polishing/focusing a particular area.  All rocks will have gaps and such so do not worry to much over little details.  As you do this more you will get better in preventing them, but I think they serve a nice educational purpose for now. 

Moving onward, we gotta think OK what do we want this rock to look like?  Think hard because after this point it is quite impossible to go back.

For first timers, continue with the sphere shape rock idea.  If this is not your first time, from the start you should of been aiming for a geometric shape(or well any shape you can think of) instead of a sphere.  I had a batch of students try to make a heart recently since it was Valentine's Day all month long.  Most did not turn out to well so I would suggest stick with the round rock first to get the feel of it first and than branch out. 

After you have decided on the shape continue steps 1-3.  The order does not matter much but rather what is needed per situation:

1.  Point the angle edge of the rock on your smooth surface and gently start to round them out(unless you want them)
2.  Rub and polish over and over.  Avoid putting to much pressure, this will create giant concave surfaces or will flatten your rock which cannot be undone.  See picture. 
3.  Continually turning/rotating your rock to assess the overall shape of your rock.

Step 5: Problems Solving and Tips

Troubleshooting:

Crevices: 
Personally I like to keep a few in the rock to talk about plates and such.  To close up a crevice, put pressure on one side of the gap and firmly start rubbing that area against the table to close the gap.  Switch to the opposite sides and continue the same.  Some gaps cant be close and that's fine, rocks are not meant to be perfect although many try. 

Weird shape
Many times a weird shape is formed when too much pressure is added typically a student will squeeze very hard while polishing and we get a concave thumb imprint or a very flat rock.  If the shape is like a bar magnet, take a scissor, cut off a piece and try to salvage it as a square rock.  Polish the cut edge and hope for the best.  For the concave issue, I've never really found a good way to fix it, just make it a feature of your rock. 

Very rigid edges 
Gently turn the rock with the edge on the table and simply gently polish it against the table, some individuals put way to much pressure.  So take it easy with the polishing. 

Tricks:
Using a constant up and down motion is not always the best choice.  Sometimes a rocking/sweeping motion that uses your wrists creates a better polish and contours to your rock's curve better. 

Alternative Technique I call Rolling:

So if you are pretty happy with your rock, it is mostly compact and just want to try another way to polish it a bit more try the below method.  I used this to finish out the tiny rock I used in the introduction. 

1.  Take the rock place it on the table,
2.  Place the palm side of your hand over it
3.  Roll in the ball in irregular circles while adding light pressure
4.  Check every min or so and do some spot polishing and continue.

Hope you enjoyed, get the students to do a lab write up, explain the process, and make some measurements and diagrams!