7cm x 4cm  
This is the largest speciman of the rare manganese borophosphate, Seamanite, that I have for sale. 
The green arrows point to patches of this rare mineral, the bottom patch being quite a bit larger than most other specimans. Seamanite was mostly found as microscopic sized crystals and larger specimans with seamanite visible to the naked eye were rare. This mineral was identified in 2000 and the mine closed in 1997,  plus the area was mined out. Surviving specimans were only found in previously collected material.