The cracks are ok, could be a little bigger, but it's also hard to know which side of the cursor to aim for the cracks as, at times, the left and right edge don't work as expected.

Everything else is good!

Dang this is awesome! What a great concept for a game. 
1. Not sure which crack you're talking about. The big one going across the geode? Or the little one I'm trying to hit in the little 'quick-time' event. If it's the big one then yeah the glowing effect is quite clear. But the little yellow cracks could be a little  longer maybe.
2. Aiming for the cracks is super satisfying and a great mechanic, however It needs more tolerance acceptance for the clickable area. Sometimes it looked like I hit it perfectly and I miss - which makes it annoying haha.  But the sounds work great with building a combo of clicks.
3. Yeah, pretty keen to keep progressing, mostly out of curiousity to see how the game gets more complex or how much depth there is to discover.

I'll also say I agree with wburd about the cursor. From using a computer I'm assuming the top left of the hammer is the clicking point. I wonder if it would read better if the animation rotated from the top left of the cursor art, so the pivot would top left or the cursor artwork (just an idea idk)