Thunderegg agate is neither an agate geode nor a simple agate. The thunderegg is, in fact, a specific geological structure. A Thunderegg can be called a geode if it contains a cavity, but not all geodes are thundereggs. Thunderegg agates usually contain chalcedony centers with agate, jasper or opal deposition. Quartz and gypsum crystals are also frequently encountered, as well as various other growths and mineral inclusions. Thunderegg agates look like ordinary rocks on the outside but, if cut in half and polished, they can reveal particular patterns and colors. A feature of thundereggs is that (like other agates) the individual beds they come from can vary in appearance, although they may retain a certain specific identity within them. They are found all over the world, wherever the necessary conditions are created. In the United States, Oregon is one of the most popular locations. Germany is also an important center, especially at sites such as St Egidien and Gehlberg.
Dimensions
Height (cm): 2-3
Depth (cm): 1-1.5
Width (cm): 3-6
Weight (g): 20-50
Property
Chemical Formula: SiO2
Mohs scale: 6.5-7
Relative density: 2.6
Crystalline System: Trigonal