Geodes

Sometimes within old lava fields are found rounded “geodes” of silica often with a rhyolite exterior.  These are known as agates, or Thunder eggs. Much like human beings, these geodes are built on the same basic pattern but each one is different from all the others. The silica is in the form of tiny microscopic crystals of quartz in a fibre or overlapping plate like configuration, known as chalcedony , agate and jasper being examples of this form of silica.

The outer part of agates often contain beautiful coloured bands and in the interiors are fill to a greater or less extent with macrocyrstalline quartz. Agates are found in many parts of the world, each have its own special variations/characteristics.
Australian Agates

Australian Agates

Argentinian Agates

Argentinian Agates

Botswana Agates

Botswana Agates

Brazilian Agates

Brazilian Agates

Lake Superior (America) Agates

Lake Superior (America) Agates

Dryhead Agates

Dryhead Agates. Interesting, these agates were formed in a sedimentary rather than igneous rocks.

German Agates

German Agates

Mexican Agates

Mexican Agates

Sometimes the agate is star shaped and without escapes tubes and often, but not necessarily, without the hollow/ macroquartz centre. These are known as Thundereggs, from the ancient native Indian legends that when the gods that lived in the region between Mount Hood and Mount Jefferson were angry , they hurled these spherical rocks at each other during thunder storms.
Thundereggs

A collection of Thundereggs

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