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Dwarves' Earth Treasures Museum:
"Mexican Coconuts"
Las Choyas & Mesteno Ranch, Chihuahua, Mexico
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    They were called "Mexican Coconuts" because of their nearly perfect spherical shapes, and they tend to be either filled with white to gray agate or lined with quartz crystals, hence "geode". The colors of agate are typically white to gray, sometimes with light bluish hue with some coming with very strong shadowing effects. The most prized of any Mexcian Coconuts would be those with deep purple amethyst geode center with clear calcite crysatals as well as those agates in any colors beside white, gray and blue colors. I have seen some with yellow agate with bits of red. Even they have been produced in adundance, very small percentage of them actually would produce any solid quality agate and amethyst geodes. I cut a crater full of "Mine run" Mexican Cococnuts(55) and got only four "Coconuts" containing solid agates. Rest are just low quality geodes, solid quartz cores, and solid geothite & calcite cores. Some "Coconuts" contained weird sagenite-like structures.
    There are several underground mines such as Mestano Ranch and Las Choyas that bring out the "Coconuts" from the clay bed under the rhyolite bed. I have obtained some clues that the "Mexican Coconuts" may have been a form of fully expanded thundereggs resulting from the rhyolitic & pertilic lava flowing over something very wet. Something wet (aquifer?) under the rhyolitic & pertilitic lava flow provided an adundant source of water vapor that would fully expand the cavities within cristobalite nodules just like the thundereggs in balloon-like manner. I wouldn't be surprised that the pertile lava flow was so enriched in water that it decomposed into clay layers very quickly providing the source of minerals that would fill the cavities of "Mexican Coconuts". I am managed to find one "Mexican Coconut" with rhyolite attached to it which is a good evidence, and it has been donated to Paul "Geodekid" Calburn for purpose of science studies on the formation of thundereggs.
I also found another Mexican Coconut with thing but intact rhyolite shells that support the idea that they are in fact the thundereggs!.
Cut specimens, 
(thin thunderegg shell around it on calcite band))		 Rough look, stretched look 
wtih some "rock bubbles"
This pair is the reason why I placed "Mexican Coconuts" in thunderegg category.
The pair came with thin but intact rhyolitc shells typical of thundereggs which get stretched thin due to expansion

YOU CAN CLICK ON THE PICTURES TO SEE LARGER PICTURES

Rough Appearance: "Coconuts" with shalllow ridges and "craters" all over, comes with dark, greenish or white skins
Some are geodes, others are solid agates in white to gray with bluish tint, any other colors are extremely rare and


Outstanding Dark Amethyst Geode with Clear Calcite Crystals.
from Las Choyas Mine

Typical Agates with shadowing effect Typical Agates from Las Choyas Mine
Rare yellowish brown agate rims Eye-catching Agates
Rare colors Rare colors
Rare purplish and yellow colors Crazy patterns
Extreme shadowing and amethyst center Classic agate-rimmed Amethyst Geodes
 
You can see some "Mexican Coconuts" for Sale at the Online Agate & Thunderegg Shop