THE SHIMMERING CAVERNS · ROCKLING
Igneous Rocks
Quartz Mirror Hall
Learn with Rockling, then use your clues in the adventure. Pause whenever you need time to read or think.
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Your Quartz Mirror Hall adventure
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Rockling — Igneous Rocks Quartz Mirror Hall
Hey, explorer! I'm Rockling. Welcome to Quartz Mirror Hall.
I keep our comparison samples on these sturdy worktables.
The Grumblies mixed up the cooling records. I need your help.
Here's what I know: rocks can begin as melted material.
Melted rock beneath Earth's surface is called magma.
When it reaches the surface, we call it lava.
Magma below. Lava at the surface. Same idea: melted rock.
When molten rock cools and becomes solid, igneous rock forms.
That beginning makes igneous rocks different from sedimentary rocks.
Granite is an igneous rock with crystals we can often see.
Common minerals in granite include quartz, feldspar, and mica.
Magma underground often cools slowly.
Slower cooling gives mineral crystals more time to grow.
Those larger crystals help tell a cooling story.
Hmm... a rock can hold clues to its past!
Lava at the surface usually cools faster than underground magma.
Faster cooling often produces very small mineral crystals.
Basalt is a common fine-grained igneous rock.
Its crystals can be too small to see easily.
Some molten rock cools into natural volcanic glass.
Obsidian is an example. It doesn't have ordinary visible mineral grains.
Glass lacks the orderly crystal structure that minerals have.
Cooling conditions influence texture: grain size and how materials fit.
Color alone doesn't tell us how an igneous rock cooled.
Let's compare the samples with their cooling records.
Two similar melts cool. One cools slowly; one cools quickly.
Which gives crystals more time to grow? Take a moment.
The slowly cooling melt gives crystals more growing time.
Well reasoned! Time helps explain the crystal-size difference.
Let's gather our clues. Magma is below Earth's surface.
Lava reaches the surface. Cooling molten material makes igneous rock.
Slow cooling often allows larger crystals to develop.
Faster cooling often produces smaller crystals, or sometimes glass.
Our mirror hall still needs an observant helper.
Use the cooling clues in the adventure. You've got this.
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