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Dwarves' Earth Treasures Museum:
Trancas "Geodes" Thundereggs
Trancas Mine, Chihuahua Province, Mexico
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.   Trancas Geodes are one of many geodic thundereggs coming from Mexico and they're popular for the purpose of "Geode-cracking" which exposes the hydrothermal quartz crystals often in very weird shapes such as "fingers", "mushrooms", and "Scepters"  It appears to me that a small percentage of the Trancas "Geode" thundereggs contain black to white agates sometimes with pink to orange colors. I don't know how rare those kind of agates are since they may be been ignored by the Mexican miners who were looking for hollow geodes. Many Trancas "Geodes" has some rhyolitic shells still attached to them, a good evidence that they were formed in the same manner as the thundereggs and that's why I listed those geodes under "Thunderegg" section.

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Rough Appearance: "Rotten coconuts" with brownish thunderegg shells
Most are geodes lined with weird hydrothermal quartz crystals, black to white agates seem to be rare(?)


Rhyolite shell attached to the agate is an evidence that the Trancas Geodes are actually fully-expanded thundereggs.
Can be applied to how "Mexican Coconuts" were formed since they have same features.


With partial thunderegg shell attached Rare colors
Rare orangish color