Q&A for How to Identify Igneous Rocks

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Is a smooth black stone I found on an old construction site likely to be an obsidian?

Community Answer

It could be, it depends on your location. If the rock has a glass-like texture or if you can see rings in it, it is very likely to be obsidian.

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How do I differentiate between granite and diorite?

Community Answer

Granite is a felsic intrusive rock and always has a red to pink or orange hue to it depending on how much K-spar it contains. Diorite is an intermediate intrusive rock which has a salt and pepper appearance.

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How many layers does an igneous rock have?

Community Answer

The common igneous rock (not including obsidian) has between 8 and 13 layers.

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Question

Who can I find to identify my rocks?

Community Answer

Contact the geology department of a college in your area, or search the Internet for options. Someone may be able to identify your rocks based on images and your descriptions.

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Question

Where can I find them?

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You can mainly find them in mountains and at high altitudes but anywhere there is open land is a good place to start.

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Question

Can I find igneous rocks in or near extinct volcanoes?

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That depends on your luck, but theoretically you should be able to.

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How can I decide whether or not an igneous rock formed from a volcanic eruption?

Community Answer

Extrusive igneous rock (that was formed after being erupted from a volcano) will have a much smaller crystal size than an intrusive igneous rock.

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Question

How can I send a picture of my rock?

Community Answer

You can send the picture via e-mail, text, social media platforms, or find a website that will allow you to send images.

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Question

I found a rock that has features of both metamorphic and igneous rock. Which one is it?

Community Answer

It depends on which specific features it has. For example, if it has parallel crystals, it's metamorphic.

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What is a rock that is black with red marble and layers of white?

Community Answer

It is a metamorphic rock. If you can visibly see different colored lines, that means it is foliated.

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Question

How would I classify a goose egg river rock?

Community Answer

Depending on the characteristics of the rock, you could classify it as either igneous or sedimentary.

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Question

If there are crystals present, how do I know if the rock is igneous or metamorphic since both types can have crystals?

Community Answer

Igneous rocks will have the crystals spread all around the rock, while metamorphic rocks have layers of crystals that are all the same size.

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What are the mineral compositions of basalt?

Community Answer

Basalt is a dark-colored, fine-grained igneous rock composed mainly of plagioclase and pyroxene minerals. It most commonly forms as an extrusive rock, such as a lava flow.

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How do I tell what type of rock I have?

Community Answer

Look at the rock closely. See if it has layers or crystals. Look at the grain patterns and the grain in general. Use a rock identification book or chart to help you.

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