My (formerly!) missing mineral is in the same spot in the museum as yours...I don't think they fill in in alphabetical order or anything, I think they fill in in the order you find them from the inside to the outside.
The tourmaline is big, two-pointed like quartz looks, and has red - white - green horizontal stripes from bottom to top.
Also, OMG, thank you so much Aviatrix, I now have a completed collection and was
rewarded with 500 coins for doing it!