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Crack Open A Thunder Egg For A Beautiful Surprise (That You Can't Eat)

The thunder eggs has been the state rock of Oregon since 1965.

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Eleanor Higgs

Eleanor Higgs headshot

Eleanor Higgs

Digital Content Creator

Eleanor is a content creator and social media assistant with an undergraduate degree in zoology and a master’s degree in wildlife documentary production.

Digital Content Creator

EditedbyFrancesca Benson
Francesca Benson headshot

Francesca Benson

Copy Editor and Staff Writer

Francesca Benson is a Copy Editor and Staff Writer with a MSci in Biochemistry from the University of Birmingham.

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Brown bobbly outer is filled with shiny blue layer that diagonally appears through the rock.

Formed from volcanic lava, thunder eggs may look plain on the outside but hide secret crystals within.

Image Credit: Lech Darski via Wikimedia Commons (CC BY 4.0)

Welcome to the wonderful world of thunder eggs. They might look plain from the outside, but can be cut and polished to reveal a whole range of colors and crystals within, and are popular with the rock collecting community. 

Thunder eggs, also known as lithophysae, are spherical objects formed in silica-rich volcanic rock, often a rock called rhyolite. 

The name “thunder egg” is said to originate from Native American folklore that says these rounded rocks were the eggs of the mythical thunderbirds that created thunder and lightning during storms, hence the name. Other legends suggest that thunder eggs were thrown during thunderstorms by warring “thunder spirits" who lived on Mount Jefferson and Mount Hood.              

All thunder eggs start life as volcanic lava. As this lava cools, material is trapped around gas bubbles. Over time, these gas bubbles crack and allow the gas to escape, leaving behind a hollow cavity. Silica and other minerals including feldspar from volcanic ash can be deposited in this cavity, hardening to deposit near solid cores of chalcedony or agate or quartz crystals which form the core of a thunder egg. The minerals often grow outwards from the center of the cavity, forming radiating structures called spherulites.

Reddish brown circle rock with a star shaped white fill on the inside. Polished and quite shiny.
The hollow cavity is filled with crystal structures or layers.
Image Credit: Wirestock Creators/Shutterstock

Some thunder eggs can be identified based on their crystal composition and the naturally occurring minerals in the area. For instance, the Del Norte Area in Colorado is known for thunder eggs containing plume and moss agate. 

There is some confusion surrounding the difference between geodes and thunder eggs. While some suggest geodes are any rock with a void inside and thunder eggs are solid, some suggest that thunder eggs are different because they were formed only by lava flow while geodes can be formed in many different ways.  

Thunder eggs can be found all over the world. The most common place to find thunder eggs in the USA is Oregon, where thunder eggs have been the state rock since 1965. 

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.  


ARTICLE POSTED IN

nature-iconNaturenature-iconenvironment
  • tag
  • geology,

  • rocks,

  • environment,

  • crystals

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