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Quarantine Quarrying: Igneous Rocks

Hello! David Olli, live science catalyst, here. Now’s the perfect time to start a collection with common rocks and minerals you can find in Virginia, if not right in your own backyard. 

There’s so much to say about rocks and minerals here in Virginia that we’ve broken up this post into a few parts. Here we’re going to cover igneous rocks. In other posts, we’re exploring sedimentary rocks, metamorphic rocks and minerals. Then, after you learn all about the different types, you’re ready to start a collection…and we have some tips on how to do that here.

Igneous rocks are formed when molten or liquid rock below (magma) or on the surface (lava) cools and solidifies. Virginia has lots of varieties of igneous rock that you can find.  

Obsidian

You may not find obsidian in your backyard but you have probably seen examples as it was used for ancient cutting tools and arrowheads. This lava cooled so fast there wasn’t enough time for dark minerals to grow into big crystals, hence the black glassy appearance. Rocks and minerals can break in unique ways depending on the molecular structure and alignment of the minerals. Obsidian exhibits what is known as conchoidal fracturing, or chips like a thick piece of glass. 

Basalt

This very fine (small) grained, dark rock called basalt is exposed in many areas of the Blue Ridge Mountains. At a relatively shallow depth, its magma took a little longer to cool allowing time for small crystal growth. Ocean floor rock is often made of basalt.

Granite from Chesterfield County Virginia

This coarse (large) grained, lightly colored rock called granite can be found all over Virginia, from the mountains to Richmond and beyond. Granite formed from magma cooling deep below the surface allowing even more time for bigger crystal growth. Granite is a good example of a rock to see individual minerals within it. Translucent grains are often quartz, alongside solid white and pink feldspar, and dark flecks of hornblende, pyroxene, amphibole, green olivine or shiny mica, a very common mineral you’ll find in rocks or soil (there’s more on that later). 

Besides exploring rocks, sharing science and eating cookies, I love to hike, especially in the mountains. If you've ever climbed Old Rag Mountain located in Madison County, those are big boulders of granite you scrambled up before standing on them at the top. Big granite boulders are also at the summit of the Sharp Top Trail through Peaks of Otter outside of Bedford. You may also have walked across and sat upon huge blocks of granite along Richmond's James River.

Thanks for exploring Virginia igneous rocks with me today. You’re now ready to try to find some! Don’t forget to check back for details about the other types.

Featured image via Getty Images

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