Stibnite altering to ??? (LATE 1700's)

Item Description

A VERY RARE LOCALITY SPECIMEN! I have never seen, even, a Moroccan stibnite and one imagines this must have been from surface oxide zone workings that are now just vanished. The weight is off, and the luster as well, so I suspect there is some pseudomorphing in process replacing the original stibnite with a lighter weight mineral (i do not know what). This collection in the Sorbonne has labels dated to the late 1700s and early 1800s, as you can see in the Covelline specimen from the same collection dated to 1760 a few items down the list here...