Saturday, April 22, 2017

Sedimentary Rocks

Our seventh Geology lesson with our co-op was on sedimentary rocks.  Following this lesson, we will have our sedimentary rocks lab, but this day was all about understanding sedimentary rocks -- how they are formed, their characteristics, and different types.
All year we have been working on a large lapbook for this course.  Occasionally, we add fun stickers like we did this one!
 After we talked about the general definition for sedimentary rocks, we put this printable in our lapbooks (from which opens to reveal the answers to the tabs.
Sedimentary rocks tend to be softer than other rocks and break more easily.
 It was time to move on to some examples of sedimentary rocks.  The first I wanted to teach them about was limestone.  I asked each child to draw a sedimentary rock on the chalkboard.  I then told them that not only did they each draw a sedimentary rock, they drew WITH a sedimentary rock! Chalk is a sedimentary rock!  They were astounded!
Our first sample for the lesson was this simple piece of limestone.  Limestone is a common sedimentary rock made up mainly of the mineral calcite.  That is because it is made up of the shells and skeletal fragments of marine organisms such as coral and mollusks.  Because that is what limestone is made of, you can frequently find fossils in it.  Limestone is also what was used to build the pyramids at Giza.  (The outside structures consist of 5 million blocks of limestone!)
 To help them remember that fossils are found in limestone, I challenged them to use a fossil rubbing plate (from my Roylco Fossil Rubbing Plates pack purchased at Amazon at to rub the image of nautilus shells onto paper inside a rock outline.
Here is the rock outline I gave them, below.  (I made this simply on my computer.  Click on the image itself to see it larger.)
 They each picked out a crayon color and rubbed the image onto their rocks.  The finished rocks turned out great!  They added this, too, to their lapbooks.
From there, we looked at our second sample, shell limestone, containing the fossil of a shell.
 Our third sample was crinoidal limestone.  Crinoids are marine animals that look like plants (below).
They are held up by stalks made of individual columnals.
 Here are fossils of those columnals that make up the stalks.
Here is an image from a Google image search of a piece of crinoidal limestone.  You can clearly see the columnals.
And here is my sample.  The children searched for those same round structures in our piece.
 They were also fascinated to learn that limestone is responsible for stalactites and stalagmites in caves.  They are formed from groundwater that contains dissolved lime and as it drips from the roof of a cave, it leaves a thin deposit as it evaporates.  This is the work of many, many years.  But these structures, too, are limestone.  One of their homework assignments (described later on in this post) will demonstrate this.
Our next sedimentary rock sample to discuss was sandstone.  Sandstone is the official state rock of Nevada.  It has massive formations of sandstone, as you can see in this picture.
Our sandstone sample has quartz in it, so it is called quartz sandstone.
 The third sedimentary rock we covered was conglomerate.  Conglomerate is made of many things, including sand and pebbles.  It is usually found in riverbeds or other bodies of water.  That is why the pebbles in them still look whole and rounded.
My sample is not great, but you can make out a few whole pieces.
 Unlike conglomerate, breccia has stone fragments that are very angular.  That's because breccia is formed at the foot of cliffs or steep mountains, so its fragments had a much more difficult erosion.  They didn't roll along a river like the conglomerate's sediments.  They took a tumble down hard rocks!  
 We also looked at siltstone, with grains that are a little finer than sandstone. 
 And what's finer than silt?  Clay!  That brought us to our shales, made up of fine clay sediments.  This first sample is oil shale.  It doesn't contain oil, but it does contain kerogen, a form of fossil fuel similar to coal.
 The second shale sample we investigated was this piece of tuffaceous shale.  The word tuffaceous refers to any rock that contains more than 50% of tuff, or volcanic ash.  So this rock is at least half volcanic ash.  You can clearly see the layers in this rock.
After we finished passing around our samples, we put together our sedimentary rocks pocket (also printed from  In it, we put the printed paddles for the samples we discussed, as well as stickers for some of these rocks that we got out of ...
... our Learning About Rocks sticker book from Dover (purchased online).  The children loved guessing which sticker from the sticker sheet matched each labeled piece of paper I made.  Conglomerate was the easiest to spot!
For lunch, I challenged the children to create and label a "Sedimentary Sandwich," with different sandwich makings representing a layer of sediment.  Beforehand, I made these sheets so they could record what was in their sandwich.
The layer boxes on the sheet would be filled with these stickers I made to represent each item/layer of their sandwiches:

 Bread was "sand."
Peanut butter was "clay."
Grape jelly was "quartz."
Strawberry jelly was "feldspar."
Chocolate chips were "gravel."
Marshmallows were "calcium carbonate."

They could put their sandwiches together in any combination they wanted, but it had to be edible and they had to record each layer on their sheets.  (They loved this activity.)
Each child had a separate space to work in.  Their plates were called their "riverbeds."
(Here was my completed example sheet to show them.)
This was fun and so much tastier than a regular, old PB&J!
Maggie's sedimentary sandwich, in the works!
Cemented together and cut in half, she was able to see the layers more clearly for her final drawing!
Looks great, Mags!
She was very proud of her delicious work!
After lunch, I gave them their homework.  The first assignment was to create a comic strip to illustrate what they had learned about sedimentary rocks.
I offered this one I made as an example, personifying chalk.  (You can click on the image to see it larger.)
 Maggie chose to draw/write her comic strip from the perspective of conglomerate rocks.  (Click on the image itself to see it larger.)
The second assignment was to complete an experiment to demonstrate how limestone creates stalactites and stalagmites in caves.  I gave them each a setup sheet, below (click on it to see it larger) ...
... and an experiment sheet for recording what they saw in their demonstrations.
We set up our experiment with the things needed.
Here, Mags is preparing our salt solution for our glasses.
Now we must wait a few days before stalactites start forming.   (I will update this post after our experiment is complete.)
Up next?  Our sedimentary rocks lab ("Sedimentary Study" with three "Sedimentary Stations") and our lesson on metamorphic rocks!  Stay tuned!

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