Boxwork

Boxwork is an uncommon type of mineral structure, or speleogen (similar to a speleothem, but formed by erosion rather than accretion), occasionally found in caves and erosive environments. Boxwork is commonly composed of thin blades of the mineral calcite that project from cave walls or ceilings that intersect one another at various angles, formin...
Found on http://en.wikipedia.org/wiki/Boxwork

boxwork

in geology, honeycomb pattern of limonite (a mixture of hydrous iron and manganese oxide minerals) that remains in the cavity after a sulfide mineral ...
Found on http://www.britannica.com/eb/a-z/b/102
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