Does dark sapphire still spawn in your backpack when mining? I haven't been able to find any.
Is your tool set to ore and gems ?
You do not need to set the pick or shovel to mine for gems. You can set it at ore or ore and granite and the special gems will still drop in your backpack. You just need to be at GM. Wearing mining gloves also helps.
Isn't there a book you also have to read
The book is only for mining normal gems. Per the wiki: The book ‘Mining for Quality Gems’ bought from a blacksmith in Royal
City allows normal, jewelry gems, to be found randomly when mining with
the tool’s context menu set to ‘ore and gems’.
I've always called the ML gems super gems just to differentiate as they are totally different and separate from actual gems