What is a Geode?
The formation of Geodes takes place over millions of years and involves several different geological processes.
Hollow Rocks
So, let’s start at the beginning: how do you get a hollow rock with lots of sparkling crystals inside? Geodes start their lives as a hollow bubble inside a layer of rock. The bubble could be from air inside explosive volcanic rock or it could come from the hollow remains of animal burrows or tree roots.
What About The Crystals?
Geodes that form from air bubbles inside of volcanic rock are pretty easy to picture. Think about the small air bubbles you see in pumice. Now, imagine just one of those bubbles completely surrounded by black or red volcanic rock. As rain pelts down on the hot bubble, the chemicals in the rock are slowly released into the water. Some of the water soaks through the hard, rocky outside of the bubble and is trapped for a moment on the inside. As the mineral-rich water moves on through the bubble, tiny crystals are left behind, clinging to the sides of the bubble. Millions of years pass while this in and out flow of water gradually builds crystals inside the empty space. The crystal formations might become large single crystals or tightly packed micro-crystals, so small that you can’t even distinguish one from another.
An Animal’s Home
Let’s check out the development of our animal burrow bubble… Long after the animal has moved on or the tree has died and its roots have rotted away, the sediments that surrounded the hollow are being covered up by layers and layers of sediment hundreds of feet think. Eventually the weight of these layers has caused the sediments to turn into rock: sedimentary rock. Just like our volcanic bubble, this animal burrow bubble is host to mineral-filled water flowing in and out through the hollow space. And just like the volcanic bubble, a wide variety of crystals are taking shape inside the animal’s former home.
Time Marches On
Fast forward to modern times. The water-soaked land where our bubbles began has become a vast desert where wind howls and the sun beats down. The ground, covered by rocks and scrubby brush yields up unusually shaped rocks. Today, you’ve found a good field of them and have three nearly-round specimens to crack open when you get home.
All Geodes Are Not Created Equal
The first one is quite hollow but for a nice layer of medium-sized blue crystals. These dugway geodes have bands of blue and pink. The colors come from the different minerals that flowed through the bubble so many millions of years ago. Another specimen is nearly solid all the way through. The microcrystals have formed wide bands of different colors and the tiny opening at the center has a thin ring of pointed crystals. Yet another is completely filled with solid rings of browns, reds and pinks. So, you’ve really found two geodes and one nodule. Nodule is the name for these round forms when they are filled solid.
Quartz, Calcite, Or What?
Most geodes have interiors made of either quartz or calcite. Quartz Crystals are silicates. Silicates are the most common mineral in the crust of the earth. Over 90% of the minerals present in earth’s crust are silicates. With this said, you can imagine that silicates are a pretty big group with lots of variation in terms of specific chemical composition.
Calcite’s main ingredient is calcium carbonate CaCO2: dissolved calcium and carbon with some of the oxygen from the water thrown in.
Small variations Can Make A Big Difference
Now, add in a trace of iron or magnesium or copper and, voila, you have color variation.
Magnesium traces in calcite forms a nice pink dolomite layer, while magnesium in silicate accounts for the purples of amethyst.
Heat Can Change It
Now if your geode was close to a lot of heat, that could change the color, too. An amethyst that gets a lot of heat loses its purple color and becomes a soft yellow or citrine. You can see why there are so many color possibilities.
A Day In The Life
So, that little geode you’re holding has had quite a journey getting to your hand. Treasure it for its beauty, but also for its history and the complex composition of minerals that made it. You’re holding millions of years of work in your hand…enjoy touching the miracle of our earth’s creation.
About the Author
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Geodes for Sale
Pink Dogtooth Calcite Geode
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STUNNING SPHERICAL GEODE OFAMETHYST WITH CALCITE CRYSTALS $24.99 |
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EXCELLENT CALCITE CRYSTAL IN BLUE QUARTZ MATRIX GEODE $9.99 |
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Brown calcite on quartz matrix in geode $50.00 |
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Cubical crystals of calcite on sky blue chalcedony in geode $50.00 |
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AMAIZING CALCITE LAYER WITH FULL OF QUARTZ CRYSTALS GEODE $99.99 |
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ROCKING CALCITE CUBE IN CHALCEDONY GEODE $9.99 |
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Calcite Faceted Pendulum w/Geode #1 $11.95 |
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SUPERB FORMATION CALCITE ON DARK BLUE AMETHICS IN GEODE $19.99 |
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WORLD CLASS GIMMY CALCITE WITH GOOSECREEKITE IN QUARTZ MATRIX GEODE $99.99 |
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SUPERB CALCITE CRYSTAL IN QUARTZ MATRIX GEODE $19.99 |
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STUNNING CALCITE CRYSTAL IN QUARTZ MATRIX GEODE $19.99 |
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KEOKUK Iowa GEODE Quartz UNOPENED Crystals HEALING STONES Calcite Rock $9.99 |
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KEOKUK Iowa GEODE Quartz UNOPENED Crystals HEALING STONES Calcite Rock $9.99 |
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4 lbs. 7” Stunning Large Cubed Calcite Crystal Filled Geode, Keokuk, Iowa $49.99 |
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UNIQUE AMETHYST GEODE/W CALCITE AND MINERAL AMG-4027 $2,318.00 |
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Nice Calcite Cluster From Geode Plate Brazil $19.99 |
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Flower Amethyst/ Calcite Geode 590 grams / 1.3 pounds ! $49.95 |
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STUNNING RED FLUORITE BALLS ON CALCITE QUARTZ MATRIX GEODE $59.99 |
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RARE MONUMENTAL & WIDE CITRINE GEODE – WITH CALCITE CENTER CLUSTER – BRAZIL $795.00 |
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WORLD CLASS GOLDEN CALCITE CRYSTALS IN BLUE MATRIX GEODE $245.00 |
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BEAUTIFUL CRYSTALS OF CALCITE ON QUARTZ MATRIX IN GEODE $24.99 |
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NICE CALCITE CRYSTAL IN QUARTZ GEODE $19.99 |
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INCREDIBLE CALCITE CRYSTAL IN QUARTZ BASE GEODE $99.99 |
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STUNNING CALCITE LIKE MICA IN CHALCEDONY GEODE $49.99 |
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AWESOME HUGE GEODE OF CALCITE LIKE MICA IN CHALCEDONY $99.99 |
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INCREDIBLE BIG SIZE CALCITE ON FLORITE IN GEODE $199.99 |
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MAGNIFICENT PRISMATIC CALCITE ON CHALCEDONY IN SEMI GEODE $9.99 |
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MIND BOGGLING OKENITE BALLS IN AMETHYST GEODE WITH CALCITE $124.00 |
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GORGEOUS CALCITE CRYSTAL ON DARK AMETHYST GEODE $249.99 |
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STUNNING BLOOD RED FLUORITE BALLS ON CALCITE IN QUARTZ SEMI GEODE $99.99 |
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HARD OKENITE BALLS WITH CALCITE ON AMETHYST IN GEODE $99.99 |
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STUNNING CONICAL CALCITE CRYSTAL IN GEODE OFSPIRKING CHALCIDONY $70.00 |
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SUPERB GOLDEN FLUORITE ON CALCITE IN SEMI GEODE OF M M QUARTZ #4854 $69.99 |
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CALCITE WITH BUNCH OF FLUORITE ON QUARTZ GEODE #3170 $200.00 |
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SUPERB HONEY CALCITE WITH FLUORITE IN SEMI GEODE OF BLUE M M QUARTZ #5015 $149.99 |
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AWESOME CALCITE CRYSTAL IN QUARTZ MATRIX SEMI GEODE $6.99 |
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Fine CALCITE crystals in a geode $160.00 |
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DAZLING NEW FIND CALCITE IN GEODE LIKE MICA $9.99 |
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CALCITE crystals in geode – MOROCCO !! /gc590 $19.90 |
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AMETHYST GEODE SPECIMEN CALCITE CRYSTAL FLOWERS AC-114 $298.00 |
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RARE TINY FLOWER OF EPI STILBITE GROWN ON CALCITE IN GEODE OF MM QUARTZ #5173 $60.00 |
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Tremolite Crystals geode in calcite matrix $40.00 |
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CLASICAL SPECIMENT GEODE OF CHALCIDONY WITH STALACTIDE CORAL WITH CALCITE CRYSTA $59.99 |
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EXCILLENT CALCITE CRYSTAL WITH MM QUARTZ IN GEODE OF CHALCIDONY $49.99 |
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POKER CHIP CALCITE GEODE WITH QUARTZ $15.00 |
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Calcite Crystal Geode Piece from Morocco $2.99 |
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Druzy Calcite GEODE White Sparkling Crystals Morocco $7.99 |
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Rock Candy Geode with Calcite and Clear Quartz Crystals $2.49 |
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Calcite Crystal Geode Piece from Morocco $2.99 |
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SUPERB GIMMY CALCITE CRYSTAL IN QUARTZ MATRIX GEODE $19.99 |
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Gem Like Calcite crystals with Pagoda calcite tower Baby Keokuk Geode Pair !! $1.99 |
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STUNNING CALCITE CRYSTAL WITH EPI-STILBITE IN QUARTZ MATRIX GEODE $9.99 |
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Curved Golden Dolomite, Calcite rhombs, Quartz crystals Keokuk Geode Pair !! $19.99 |
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Brilliant Clear Caclite crystal group in Tan Calcite Keokuk Geode Pair !! $9.99 |
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Lustrous Gold Iridescent Brown & Clear Calcite Keokuk Geode Pair !! $4.99 |
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White Calcite & Clear Quartz Crystals Keokuk Geode Pair !! $9.99 |
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GREAT CALCITE CRYSTALS WITH SPARKLING SNOW WHITE CHALCEDONY GEODE $11.99 |
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Siaz: 5.5″ SEPTARIAN GEODE EGG LARGE ARAGONITE CALCITE sphere ball FLUORESCENT $275.00 |
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DAZZLING GOLDEN CALCITE CRYSTAL IN AMETHYST HUGE GEODE $300.00 |
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AWESOME CALCITE CRYSTAL WITH STILBITE IN QUARTZ MATRIX GEODE $19.99 |
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STUNNING GIMMY GOLDEN POINTED CALCITE CRYSTAL IN QUARTZ MATRIX GEODE $19.99 |
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STUNNING GOLDEN CALCITE CRYSTALS IN CHALCEDONY GEODE $6.99 |
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ORCHID CALCITE ROUGH QUARTZ CRYSTAL GEODE on wood base 2.3″ Feng Shui healing $9.99 |
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EXCELLENT FORMATION OKENITE BALLS WITH CALCITE IN GEODE $155.00 |
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MARVELOUS OKENITE BALLS WITH CALCITE ON DARK BLUE AMETHICS IN GEODE $195.00 |
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INCREDIBLE GOLDEN CALCITE CRYSTAL IN AMETHYST GEODE $300.00 |
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Calcite Crystal and Agate Geode from Uruguay #2100 $250.00 |
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LOT OF THREE CALCITE CRYSTAL GEODE FROM MOROCCO $10.00 |
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10.3 lb Septarian Dragon Stone Geode w/Golden Calcite, $562.00 |
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MARVELOUS OKENITE BALLS WITH CALCITE ON DARK BLUE AMETHICS IN GEODE $165.00 |
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15.6 LB Superb Geode – Quartz – Stilbite – Calcite – Heulandite – Nashik, India $180.00 |
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Amethyst Geode Cathedral “Very Deep w/ Calcite Points” $1,249.99 |
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(mn2036.003)Calcite some with marcasite(Geode) $34.50 |
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ROUGH CALCITE GEODE CRYSTAL CLUSTER APOPHYLLITE DRUZY $34.95 |
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ROUGH CALCITE GEODE CRYSTAL CLUSTER APOPHYLLITE DRUZY $29.95 |
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3.25″ KEOKUK QUARTZ CRYSTAL GEODE PAIR, CALCITE, ARAGONTIE, MINERAL SPECIMEN G9 $20.00 |
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AMETHYST GEODE CRYSTAL CLUSTER SPECMN URUGUAY w CALCITE $59.00 |
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CRYSTAL INSIDE GEODE MEXICO MINERAL DRUSY QUARTZ CALCITE #GO129 $5.45 |
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DAZLING NEW FIND CALCITE LIKE MICA IN GEODE $150.00 |
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Cut Geode with Dark Calcite Angel Wing Vugs from Mexico $9.99 |
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WORLD CLASS QUARTZ MATRIX GEODE WITH BROWN CALCITE CRYSTALS $240.00 |
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AAA URUGUAYAN AMETHYST crystal point cluster quartz geode 7.45lb With Calcite $329.99 |
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7″ Amethyst Geode Spesiment With Calcite Crystal Cluster $282.00 |
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CALCITE CLUSTER 2.4″ Crystal Geode Yellow White 05 $14.25 |
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PERFECT GEODE 1/2 W/ LARGE CALCITE BLADE DISPLAY PIECE! $9.99 |
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BIG Cut Geode With Odd Calcite Blade FILLED Vugs Stands Included $29.99 |
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Rare Fossil Amber Calcite Crystals Whelk Busycon Shell Geode Mineral Display $199.99 |
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28.5″ Dark Amethyst Calcite Crystal Geode 103.5 lbs $647.00 |
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Calcite Faceted Pendulum w/Geode #2 $11.95 |
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Green Serpentinite Gemstone Cockatoo w/ Golden Calcite Crest on Amethyst Geode! $45.00 |
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Orange Calcite Toucan Carving w/ Aventurine Bill & Tail, on Amethyst Geode! $24.00 |
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AWESOME CALCITE CRYSTALS IN QUARTZ BASE GEODE $60.00 |
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CALCITE + CHABAZITE + EPI-STILBITE IN GEODE $120.00 |
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HUGE 2lb Calcite Peach STILBITE on Snowy CHALCEDONY Geode Crystal Cluster INDIA $28.00 |
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Calcite some with marcasite(Geode) (mn2036.008) Missouri $24.50 |
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9pcs Amethyst, Amber, Calcite, Crystal, Geode, Quartz, Obsidian rock collection $8.95 |
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INCREDIBLE FORMATIO OF CALCITE LIKE STICK IN QUARTZ MATRIX GEODE $350.00 |
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Geode Of Yellow Gemmy Calcite Crystals Cabinet Sized $22.99 |
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BROWN GEMMY CONICAL CALCITE ON WHITE QUARTZ GEODE#3196 $110.00 |
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5.5″ Crystal-Filled CALCITE GEODE-Both Halves-Morocco $75.00 |