Everyday Einstein shares a few interesting highlights and surprising facts about geology. What kinds of rocks can you find in your local park?
A few days ago, my birdwatching daughters started to develop a sudden interest in rocks and minerals.
I’m far from an expert in geology, so we set off to see what we could learn together. There are a ton of great resources that I’ll link to later on, but today I just want to share a few interesting highlights and surprising facts that we discovered about the hardest of sciences. (That’s the last bad joke for this episode.).
Rocks vs. Minerals vs. Crystals
The first thing we wondered is - what’s the difference between a rock, a mineral, and a crystal? It turns out that a “rock” is made up of two or more different kinds of mineral particles. So if you take a piece of granite (a rock) and look at closely, you’ll see that it’s made up of a bunch of tiny mineral particles, mostly quartz, mica, and feldspar, with a few other minerals mixed in.
If you have a pure mineral, such as a big hunk of quartz, it will typically be in a crystal shape. That’s because minerals are all made of the same kind of molecule, and molecules that are all the same, have a tendency to line up in nice organized patterns. Our chunk of quartz is made up of a bunch of Silicone dioxide molecules (SiO₂) lined up in a trigonal crystal shape.
So to summarize, rocks are made up of two or more different kinds of mineral particles, while crystals are formed by single minerals.
The Rock Cycle
Something we’d learned about before, but that was still pretty interesting, is the rock cycle. Most people have heard of the water cycle, but did you know there was a rock cycle? Rocks undergo a constant cycle of transformation, just like water, only it takes a lot longer.
When hot magma or lava cool off, they form igneous rocks, such as granite and obsidian. Over time, wind and water erode those igneous rocks, and those eroded particles travel downstream to the sea, where they’re compressed into sedimentary rocks like sandstone and limestone.
As those sedimentary rocks get pushed further and further underground by geological forces, the immense pressure and heat transforms them into metamorphic rocks like slate and marble. Over time, these rocks eventually get pushed down further where they melt back into magma, and the cycle begins anew.
Of course the cycle isn’t always that straightforward. Sometimes a metamorphic rock will get pushed to the surface of the earth and undergo erosion, bypassing the igneous phase completely, or igneous rocks might get compacted down under the earth, turning into metamorphic rock without becoming sedimentary rocks first.
Like Sand in the Hourglass
Most people know that sand is made from eroded rocks, but now that you know that rocks are made of crystals, have you ever thought about the fact that every piece of sand on the beach is a miniature crystal? If you search the internet for something like sands of grain through a microscope, you can find beautiful photographs of these miniature crystals.
The Hardest Rocks to Identify
Of course what every budding geologist wants to do with their pretty rocks is figure out what kind they are. Unfortunately this isn’t always easy, especially with rocks that kids find. Professional geologist Hobart King has this to say on the subject:
“If you are highly skilled at rock identification I am willing to bet that there is a location near your home where your hand-specimen identification skills can be put to a rigorous test. The location isn't an outcrop. It's your local elementary school. There you will encounter a diversity of interesting rocks - many of which you will be unable to identify. It does not matter how many petrology courses you have taken or how many outcrops you have studied. You will probably be caught off-guard by what students bring to school.”
The reason for this is that unlike most geological samples, which usually seek to identify the most representative rocks for a given reason, kids are usually looking for the most interesting rocks possible.
Regardless of the difficulty level, all you need to identify minerals are a few basic supplies. First, I recommend you find a good field guide to rocks and minerals, preferably one with color pictures. From there, you’ll find a list of basic supplies and tools you can use for identifying what you’ve found, all of which you should have sitting around your house.
So those are some of the highlights of what we’ve learned this week in our geology studies. If you have more questions about geology, I highly recommend Andrew Alden’s great resources on about.com.
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