Igneous Rocks

We continued along in our Rock & Mineral study with a discussion of the Rock Cycle and the first of our rock types – Igneous. 

We usually start our demonstrations with reading the brief descriptions found on the “For my notebook” page from REAL Science Odyssey.  I like these because they cover the information in a nice, concise manner.  Since my kids don’t do well listening to a long, drawn-out explanation, these are the perfect length to keep their attention. 

This week, Georgie actually decided he wanted to read it aloud to Vicki.   Other than helping him with the pronunciation of some words, he did great.

For our igneous rock demonstration, we started by (attempting) making fudge.  Since I did not want to spend a lot of time standing at the stove, I looked up a recipe for microwave fudge.   First we mixed together our “minerals” – chocolate chips, butterscotch chips and marshmallows.  The kids couldn’t resist sampling, at least until I poured in the evaporated milk.    The “minerals” were then heated up to make “magma” (in the microwave), shot out of a volcano as “lava” (removed from the microwave and poured into a pan), which then cooled and became solid rock (putting it in the fridge).  The kids definitely got the idea about how heat changes the pieces into something new but our fudge never actually solidified so we didn’t get a treat out of the demonstration.

We then examined the three igneous rocks from our kit, plus one more.  We discussed the difference between intrusive (cooled below the surface – large crystals) and extrusive (cooled above the surface – small crystals) rocks and then identified our rocks. 

Granite is an intrusive rock that is usually speckled with black, white, or even pink, since it is made from quartz, mica and feldspar.  We can actually find granite just by stepping outside in our yard.  The bedrock under our house is all granite and rocks of various sizes show up all the time.

Basalt is an extrusive rock that is a solid, dark gray or black, with tiny holes where gas escaped.

Obsidian is one of my favorite rocks.  It’s a shiny, glassy looking black rock.  Snowflake obsidian has white flakes in it that look like….snowflakes.  Obsidian cools so quickly that no crystals form at all. 

Our last igneous rock was a piece of pumice that I picked up at the drug store.  Pumice forms when lava turns solid very quickly with trapped air bubbles in it.  Pumice is the only rock that floats in water.

After we identified our rocks, Georgie actually asked to write about his rock in his journal.   That journal is definitely something I should have started a long time ago. 

Vicki decided she wanted to bring her “field journal” into the living room to do more writing (even though her entries are nothing but wiggly lines across the page, she does talk out a good entry while she’s doing it.  One of these days, I’ll get the chance to write down her mumblings.)