The Oregon Museum of Science and Technology (OMSI) in Portland has an interesting display of Thunder Eggs. While Thunder Eggs might look sort of like rocks, OMSI says that they are really honorary rocks by legislative decree (in 1965, the Oregon legislature declared Thunder Eggs to be Oregon’s official state rock). They are really structures, sometimes nodules, sometimes geodes, occurring in rhyolite, welded tuff, or perlitic rocks.
Thunder Eggs, have a knobby exterior and look fairly nondescript. However, when cut open and polished the real soul appears in the form of colorful and exquisite designs.
According to the Museum display:
“Scientists do not agree on the processes forming Thunder Eggs. Some insist that the unique patterns of Thunder Eggs occur due to expansion and rupture of rocks by gases. Others claim that patterns are caused by desiccation (drying) of a colloid or gel. Whatever the process, after the cavity containing the egg is formed, further development is extremely variable in the amount of time needed to complete the Egg, in the degree and type of filling, and in other physical characteristics.”
In addition, to scientific explanations of Thunder Eggs, there are also mythological explanations. According to the Museum display:
“A Warm Springs Indian traditional story tells us that masses of rock were once hurled from the craters of Mt. Hood and Mt. Jefferson when the spirits of the mountain were angry. The rocks were accompanied by much thunder and lightning, resulting in the name ‘Thunder Eggs.’”
Museum Monday
On Mondays, Museums 101 provides a photo tour of different museums and museum displays. Also from this series:
Museums 101: Gems and Minerals as Art (Photo Diary)
Museums 101: California Gems and Minerals (Photo Diary)
Museums 101: The Hixon Gem Vault (Photo Diary)
Museums 101: South American Gems and Minerals (Photo Diary)
Museums 101: The Gem and Mineral Hall (Photo Diary)