Thunderegg

:"This article is about a type of rock; for the rock and roll band, see Thunderegg (band)"A thunderegg (or thunder egg) is a nodule-like geological structure, similar to a geode, that is formed within a rhyolitic lava flow.

Appearance and composition

Thundereggs are rough spheres, most about the size of a baseball - though they can range from less than an inch to over a metre across. They usually contain centres of chalcedony in the form of agate, jasper or opalcite web | title = America's Volcanic Past - Oregon | publisher = USGS Cascades Volcano Observatory | url = http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_oregon.html | accessdate = 2007-06-08] , either uniquely or in combination. Also frequently encountered are quartz and selenite crystals, as well as various other mineral growths and inclusions. Thundereggs usually look like ordinary rocks on the outside, but slicing them in half and polishing them may reveal intricate patterns and colors. A characteristic feature of thundereggs is that (like other agates) the individual beds they come from can vary in appearance, though they can maintain a certain specific identity within them.

Thunderegg is not synonymous with either geode or agate. A geode is a simple term for a rock with a hollow in it, often with crystal growth. A thunderegg on the other hand is a specific geological structure. A thunderegg may be referred to as a geode if it has a hollow in it (see illustration of Gehlberg specimen), but not all geodes are thundereggs because there are many different ways for a hollow to form. Similarly, a thunderegg is just one of the forms that agate can assume.

Thundereggs are found all over the world wherever the conditions are right. The USA, and Oregon especially, remain one of the most famous thunderegg locations. Germany is also an important centre for thunderegg agates (especially sites like St Egidien and Gehlberg). Other countries known for their thundereggs include France, Poland, Romania, Turkey, Mexico, Argentina, Canada, Australia and some places in Africa.

History

According to Pacific Northwest native legend, the Thunder Spirits lived at the highest reaches of Mount Hood and Mount Jefferson, and when they became angry at each other, they threw these spherical rocks at each other.

tate rock designation

On March 30 1965, the thunderegg was designated as the Oregon state rock by a joint resolution of the Oregon Legislative Assembly.cite web|url=http://www.shgresources.com/or/symbols/rock/|title=Oregon Symbols|publisher=SHG Resources|accessdate=2007-09-17] [http://www.leg.state.or.us/ors/186.html Chapter 186 — State Emblems; State Boundary] 2005 Oregon Revised Statutes] cite web | title = Rock Hounding | publisher = Nature of the Northwest | url = http://www.naturenw.org/rock-thundereggs.htm | accessdate = 2007-09-17] While thundereggs can be collected all over Oregon, the largest deposits are found in Crook, Jefferson, Malheur, Wasco and Wheeler counties.cite web|url=http://bluebook.state.or.us/facts/almanac/almanac05.htm|title=Oregon Almanac|publisher=Oregon Blue Book|accessdate=2007-09-19]

References