THE SHIMMERING CAVERNS · ROCKLING
Metamorphic Rocks
Gemcart Bridge
Learn with Rockling, then use your clues in the adventure. Pause whenever you need time to read or think.
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Your Gemcart Bridge adventure
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Rockling — Metamorphic Rocks Gemcart Bridge
I'm Rockling. Welcome back to Gemcart Bridge, explorer!
I check our sample cart here before crossing the cavern.
The Grumblies mixed up records about rocks that changed.
Let's take one steady step at a time. Here's what I know.
Metamorphic rocks form when existing rocks change while staying mostly solid.
Heat and pressure can change minerals and rock texture.
That is different from melting rock into magma.
Minerals can grow, rearrange, or change into different minerals.
The starting rock is sometimes called the parent rock.
It can be sedimentary, igneous, or already metamorphic.
Hmm... an older rock can begin another chapter.
Shale can change into slate during metamorphism.
Slate often splits along closely spaced flat surfaces.
Pressure can help minerals line up in a rock.
This can produce foliation: a layered or banded texture.
These patterns aren't simply new sediment piled in water.
Gneiss commonly shows bands of different mineral groups.
Those bands are clues to changes inside the rock.
Limestone can change into marble when its minerals recrystallize.
Marble commonly lacks the aligned layers we see in slate.
So not every metamorphic rock has visible bands.
Quartz-rich sandstone can change into quartzite.
The starting rock and changing conditions influence what forms.
These changes often happen deep underground over long periods.
Our bridge is a story setting, not a metamorphic factory.
We use its sample records to imagine Earth's deeper changes.
A rock changes under heat and pressure without melting.
Does that describe metamorphism, or cooling from melted rock?
Metamorphism! The rock changed while remaining mostly solid.
If it melts, then cools, the new rock is igneous.
You noticed the important difference. Nicely done!
Our first clue: metamorphism changes existing rock without melting it.
Our second: different starting rocks can produce different results.
Our third: some metamorphic rocks have aligned minerals or bands.
Others don't. A banded pattern isn't required for every sample.
Back at the bridge, our sample records are clearer.
Take your time with the adventure. You can use these clues.
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