A very nice, intuitive game! At first, the lack of any tutorial or instructions was confusing, but after the first click it was clear what we were set out to do. It feels good to get those nice, long cascades after "excavating" around certain veins! Also, I really appreciate the color choices you've got here -- as a colorblind person (not entirely, just to blues) it can be very difficult with these timed games where determining the color of a block is key! These colors were thankfully very, very distinct, and hard to confuse with one another. So kudos for that!
If I had to make one suggestion, I'd say it would be cool if there was a sort of "zen" mode, where there may be no time limit, or perhaps a random mode, with the amount of colors and shape of the piece is randomized between each level.
As a previous commentator said: from one developer to another, well done!