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

Geode

Geodes are geological secondary sedimentary structures which occur in sedimentary and certain volcanic rocks. Geodes are essentially spherical masses of mineral matter that were deposited sygenetically within the rock formations they are found in. Geodes have a Chalcedony shell containing...

, that is formed within a rhyolitic

Rhyolite

This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...

 lava flow.

Appearance and composition

Thundereggs are rough sphere

Sphere

A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...

s, most about the size of a baseball—though they can range from less than an inch to over a meter across. They usually contain centres of chalcedony

Chalcedony

Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of the minerals quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic...

 in the form of agate

Agate

Agate is a microcrystalline variety of silica, chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks and can be common in certain metamorphic rocks.-Etymology...

, jasper

Jasper

Jasper, a form of chalcedony, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. This mineral breaks with a smooth surface, and is used for ornamentation or as a gemstone. It can be highly polished and is used for vases, seals, and at one time for...

 or opal

Opal

Opal is an amorphous form of silica related to quartz, a mineraloid form, not a mineral. 3% to 21% of the total weight is water, but the content is usually between 6% to 10%. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most...

, either uniquely or in combination. Also frequently encountered are quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of 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

Geode

Geodes are geological secondary sedimentary structures which occur in sedimentary and certain volcanic rocks. Geodes are essentially spherical masses of mineral matter that were deposited sygenetically within the rock formations they are found in. Geodes have a Chalcedony shell containing...

 or agate

Agate

Agate is a microcrystalline variety of silica, chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks and can be common in certain metamorphic rocks.-Etymology...

. 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

Structural geology

Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover information about the history of deformation in the rocks, and...

. 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

Agate

Agate is a microcrystalline variety of silica, chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks and can be common in certain metamorphic rocks.-Etymology...

 can assume.

Thundereggs are found globally wherever conditions are right. The USA, Oregon

Oregon

Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

 especially, remains one of the most famous thunderegg locations. Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 is also an important centre for thunderegg agates (especially sites like St Egidien and Gehlberg). Other countries known for their thundereggs include some places in Africa

Africa

Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

, Poland

Poland

Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...

, Romania

Romania

Romania is a country located at the crossroads of Central and Southeastern Europe, on the Lower Danube, within and outside the Carpathian arch, bordering on the Black Sea...

, Turkey

Turkey

Turkey , known officially as the Republic of Turkey , is a Eurasian country located in Western Asia and in East Thrace in Southeastern Europe...

, Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

, Argentina

Argentina

Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

, Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 and France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

.

History

According to Pacific Northwest

Pacific Northwest

The Pacific Northwest is a region in northwestern North America, bounded by the Pacific Ocean to the west and, loosely, by the Rocky Mountains on the east. Definitions of the region vary and there is no commonly agreed upon boundary, even among Pacific Northwesterners. A common concept of the...

 native

Native Americans in the United States

Native Americans in the United States are the indigenous peoples in North America within the boundaries of the present-day continental United States, parts of Alaska, and the island state of Hawaii. They are composed of numerous, distinct tribes, states, and ethnic groups, many of which survive as...

 legend, the Thunder Spirits lived at the highest reaches of Mount Hood

Mount Hood

Mount Hood, called Wy'east by the Multnomah tribe, is a stratovolcano in the Cascade Volcanic Arc of northern Oregon. It was formed by a subduction zone and rests in the Pacific Northwest region of the United States...

 and Mount Jefferson

Mount Jefferson (Oregon)

Mount Jefferson is a stratovolcano in the Cascade Volcanic Arc, part of the Cascade Range, and is the second highest mountain in Oregon. Situated in the far northeastern corner of Linn County on the Jefferson County line, about east of Corvallis, Mount Jefferson is in a rugged wilderness and is...

, and when they became angry at each other, they threw these spherical rocks at each other.

State rock designation

On March 30, 1965, the thunderegg was designated as the Oregon state rock by a joint resolution of the Oregon Legislative Assembly

Oregon Legislative Assembly

The Oregon Legislative Assembly is the state legislature for the U.S. state of Oregon. The Legislative Assembly is bicameral, consisting of an upper and lower house: the Senate, whose 30 members are elected to serve four-year terms; and the House of Representatives, with 60 members elected to...

. While thundereggs can be collected all over Oregon, the largest deposits are found in Crook

Crook County, Oregon

-Demographics:As of the census of 2000, there were 19,182 people, 7,354 households, and 5,427 families residing in the county. The population density was 6 people per square mile . There were 8,264 housing units at an average density of 3 per square mile...

, Jefferson

Jefferson County, Oregon

Jefferson County is a county located in the U.S. state of Oregon. In 2010, its population was 21,720. It is named after Mount Jefferson. The seat of the county is Madras.-History:...

, Malheur

Malheur County, Oregon

Malheur County is a county located in the southeast corner of the U.S. state of Oregon. It is included in the eight-county definition of Eastern Oregon. Most of the county observes the Mountain Time Zone, although the southern quarter of the county observes the Pacific Time Zone along with the...

, Wasco

Wasco County, Oregon

Wasco County is a county located in the U.S. state of Oregon. The county is named for a local tribe of Native Americans, the Wasco, a Chinook tribe who lived on the south side of the Columbia River. In 2010, its population was 25,213...

 and Wheeler

Wheeler County, Oregon

As of the census of 2000, there were 1,547 people, 653 households, and 444 families residing in the county. The population density was 1 people per square mile . There were 842 housing units at an average density of 0 per square mile...

 counties. The world’s largest thunderegg, a 1.75 ton specimen, is housed by the Rice Northwest Museum of Rocks and Minerals

Rice Northwest Museum of Rocks and Minerals

The Rice Northwest Museum of Rocks and Minerals is a non-profit museum in Hillsboro, Oregon, United States. Located just north of the Sunset Highway on the northern edge of Hillsboro, the earth science museum is in the Portland metropolitan area...

 in Oregon. Nyssa, Oregon

Nyssa, Oregon

Nyssa is a city in Malheur County, Oregon, United States. The population was 3,163 at the 2000 census. The city is located along the Snake River on the Idaho border, in the region of far eastern Oregon known as the "Treasure Valley"...

is the Thunderegg capital of the world. Nyssa has a thunderegg festival every year during the summer to celebrate.