negative crystal inclusion in fenster skeletal crystal

This fenster or skeletal quartz crystal from brandberg has a textbook perfect example of a negative crystal inclusion. A negative crystal inclusion is a void in the shape of a crystal that is inside of a crystal. These are usually hollow airspace which may be in a vacuum, contain gas but can also be fluid filled or be fluid filled with a gas bubble and or a solid substance such as clay, oil, or another crystal such as salt or fluorite or even another quartz crystal!

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