In the world of minerals different localities can often be distinguished by variations in morphology and or associations; for example it is comparatively easy to determine that a dioptase specimen was collected in Tsumeb over say Kaokoveld or Altyn.
I believe it is more unusual to find something that is almost completely identical so as to make a visual distinction almost impossible.
During our recent trip to sort and retrieve more minerals from the Gabrys Museum we encountered the specimen above.
It is a specimen of quartz replacing octahedral fluorite and on first inspection looks almost exactly like a complete replacement specimen from Wheal Mary Ann in Cornwall; however this piece was collected some time ago at Arnbruck in Lower Bavaria.
Really hard to tell apart, see pictures below, yet both different say from specimens from Colorado.
Thank goodness for some decent cataloguing!!