Thursday, December 1, 2011

Creating a Rock Collection

My girls both love rocks and frequently come home from our outdoor adventures with pockets stuffed full.  Recently, they've taken to destroying, I mean harvesting, rocks from our decaying asphalt driveway.  The top layer of asphalt has come off at some spots and the underlying rock layer is exposed.  (My hubby and I are having issues justifying the expense of repaving...)  Rocks are fascinating to kids and they are a great way to explore some basic geology.  A rock collection is a great way to turn those finds your kids come home with into a learning experience.

Materials Needed:
  • bucket
  • digging tool
  • magnifying glass
  • sorting containers (we used plastic egg and apple cartons we pulled from the recyling bin)
  • desk lamp
  • rock and mineral guide (we used the DK Pocket Guide for Rocks and Minerals as well as a one page sheet (Google Doc) I put together comparing the different types of rocks)

Process and Pictures:

Start off by collecting a variety of rocks.  The girls collected some from around our property but you could find them a variety of places.  Outcroppings or hillsides are better places to find interesting rocks than flat land in general.  (Assuming, of course, that you don't want your child picking apart your driveway.)  Give them a bucket in which to put their finds.  You can also provide them with a magnifying glass to examine their rocks.

Bring the rocks inside and have your child spread them out in front of them.  It is helpful to have both a magnifying class for observing the rocks more closely and also a desk lamp to provide some extra light.  If you have a rocks and minerals guide this would be a great time to share it with your child; they are often fascinated by the beautiful pictures that the guides often contain.  Talk about the properties of the rocks that they can observe.  Some rocks may have visible crystals.  Some may be very monochromatic while others may have many colors present in them.  You may find a rock that has fragments of other rocks in them.  You can also have them observe the rocks using their other senses such as feeling how rough or smooth they are.  
Ask your child to sort the rocks. There are a variety of ways to sort, depending on the inclinations of your child.  One way to sort which works especially well for the youngest child is by color, which is what my younger child wanted to do.  We used a large, apple container for Maya's collection - the impressions were big enough to fit a large number of rocks.  The colors are indicative of the minerals present, which you can tie back to the mineral pictures in the guide if you want.  For younger children, you could also sort it into what they can imagine using the rocks for, similar to the book "If You Find a Rock".  Sort the rocks into groups based on what your child can imagine using them for: skipping, wishing, writing, etc. 

Another way to sort is by the crystals present in the rocks. Sydney is obsessed by the "sparkles" in the rocks - so we talked about what crystals are and how they grow.  (We may have to grow some crystals in the near future she is so fascinated by them...)  Sydney started out by sorting the rocks into those with visible crystals and then from there sorted them by those with similar color and texture.  We used a 2 dozen egg container for Sydney's collection - the impressions were smaller but able to accommodate her collection with a greater number of groups.

For older children, see if you can sort the rocks by type: igneous, sedimentary or metamorphic.   This is not necessarily an easy process as experienced rock hunters and geologists can spend hours debating the characteristics of various rocks, but you may be able to sort them based on some very general ideas related to how they are formed.  (See 'What's Happening' section below for formation information.)

Put your collection into a safe spot so that future finds can be put into the containers. You can also take pictures of the rocks to put into the child's science journal and make labels for the containers.

What's Happening:
Rocks are all around us.  They are a combination of two or more minerals.  (For more information on minerals, see the 'Extensions' section below'.)  They are classified by how they are formed into either igneous, metamorphic or sedimentary rocks.  They are then further identified based on the minerals that are present in the rocks. 

Igneous rocks are formed as molten lava cools and often have interconnected crystals of different minerals.  If the crystals are big, then the rock cooled slowly so they were probably formed inside the early.  If the crystals are small, then the rock cooled quickly on the surface of the earth.  Igneous rocks also may have pores with the gases escaped as the rock cooled.  Metamorphic rock is rock that has been transformed due to heat and pressure.  They are often denser than igneous rock and their crystals may have separated into bands.  Sedimentary rocks are rocks that have been created from fragments of other rocks that have been cemented together.  If you can see small pieces of other rocks or, even better, fossils, then you probably have a sedimentary rock.  The one page sheet I created has some pictures of common rocks for each of the three types, or you can also refer to this rock chart from the United States Geological Survey to learn more.  I also found this on-line rock key that the author has successfully used with elementary age students that you might want to give a try.


We really enjoyed the book, "Let's Go Rock Collecting" by Roma Gans.  It starts out with kids going rock collecting but talks about the types or rocks and even the rock cycle.  A good intro for young scientists out there and Maya even selected it as a bedtime reading book several days in a row.

Another thing to do that would be interesting, especially with older kids, is to see if you can identify the minerals that are present in the rocks.  For this a guide is especially helpful.  Geologists look at the following characteristics to aid in mineral identification:
  • color
  • streak
  • transparency
  • luster
  • hardness
  • cleavage
  • fracture
  • specific gravity
  • crystal form
You can find more information on each of these characteristics on the "Rocks for Kids" website.  
Maya testing the streak of one of her rocks.

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