That was changed in 1.6.9.
From the 1.6.9 changelog:
"The collections tab now shows artifacts, gems, and minerals once they’re donated to the museum (not as soon as you find it)"
www.stardewvalley.net
To be honest, It's a little confusing as the wiki directly contradicts itself
"The mineral does not need to be shipped or donated to the Museum to be registered.
Minerals and their descriptions will not appear on the collections tab until they are donated to the Museum."
The Collections tab acts like a record of which items have been discovered or shipped and in what quantities.
stardewvalleywiki.com
The wiki definitely needs to be fixed so the requirements are clear.