Fluorite (#55)

Lustrous gemmy light green cubo-octahedrons to 1 1/8" on HF etched white quartz.
North America Deer Trail Mine, Piute County, Utah 9" x 6 ½" x 6 ¼"


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We have discussed fluorite before (specimens 3, 7, 21, and 28), but what is a cubooctahedron? It is a combination of two crystal forms - and a crystal form is a collection of equivalent crystal faces. So a cubo-octahedron consists of the cube form and the octahedron form.

A crystal consisting of only cube faces would look like this:  

A crystal consisting of only octahedron faces would look like this:  
A cubo-octahedron looks like this:  

Crystals rarely have perfect shapes because of the vagaries of crystal growth, but can you look closely at the shapes of the crystals in this specimen and make out the cubooctahedral shapes?