Egg Shell Geodes
How are geodes formed? How can you make a geode in an egg
shell?
Background Information:
Geodes can be round, or they can be egg-shaped. Geodes need
time -- and a perfect combination of pressure, fluids, and dissolved
minerals in order to form. They also need a cavity of some sort
to form around. This might be the body of a sea creature that
has fallen to the ocean floor. Over many years, a marine animal
becomes buried under layers of sediment. Pressure compresses these
layers and a chemical reaction causes them to harden into rock.
Salt water can be trapped with the buried sediments and seep through
-- filing the cavity over thousands of years. Silica in the water
can form a thin wall -- like the skin of a bubble -- on the inner
surface of the cavity.
Perhaps millions of years later, as Earth's crust moves, this
part of the ocean floor may become dry land. Now, less salty ground
water can seep slowly through it -- to create quartz or calcite
crystals on the inside surface of the geode. From the outside,
the geode now looks like a rather plain, round or egg-shaped rock.
It's very hard to break open with a hammer. But when you cut it
open, you find a miniature world of crystals inside.
You can make your own geode in an egg shell. Follow the recipe below.
Procedure: Mix up a epson salt solution.
40 ml of water.
20 grams epson salt.
Initial your egg shell.
Fill an egg shell with solution.
Let stand until the water evaporates and crystals form.
Questions:
1. What are the shapes of geodes? _____________________
2. What are3 conditions geodes need to form. __________________________
______________________________________________________
3. How might a cavity form at the bottom of the sea sediments?_____
______________________________________________________
4. What kind of crystals can form inside a geode? _______________
Read the Poem below. Does this poem describe the beauty of the process of geode formation?
Opening the Geode
When the molten earth seethed
in its whirling cauldron
nobody watched the pot
from a tall wooden stool
set out in windy space
beyond flame's reach;
and when the spattering mush
steamed, gurgled, boiled over,
mounded up in smoking hills
no giant mixing spoon
smoothed out the lumps and bubbles
as the pottage cooled to rock.
No kitchen timer ticked
precisely the eons required
to fill the gritty pits
slowly, drop by drop
with layers of glassy salts,
agate, opal, quartz;
no listening ear inclined
over the silicon mold
to hear the chink of crystals
rising geometrically
facet upon facet
in the airless dark.
No hand lifted the stony lid
to add light, the finishing touch,
and no guest cried Ah! how well
the recipe turned out-
until this millennium, today,
at my table.
-Julie Alger
published in Peregrine, Volume XI, 1992
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