Breaking a diamond comes down to timing and some luck. I’ve found that breaking a diamond that’s below the line is a lot easier than breaking a diamond above the line, since you have more control over the circle when you’re bouncing it upwards than when you’re letting it fall.
To collect a diamond, you want the entire diamond to pass through the circle without touching the top or bottom of the circle. To break a diamond, you want these parts of the circle to hit the diamond. The reason it’s easier to break a diamond that’s below the line is that you can wait for your circle to reach the right point (just a little bit before the diamond) and then tap it upwards, breaking the diamond from below. The trick is to time it so that you don’t end up hitting the line too; essentially, you want the high point of your bounce from below to hit the diamond, and then have the circle follow through on its fall.
When trying to break a diamond that’s above the line, you have wait for the trajectory of the circle to let it fall on top of the diamond, which is much harder to control (although with the right timing, this can be done too). Diamonds can also be broken when the top or the bottom of the circles hits them from the side, but like breaking a diamond from above, the timing for this is difficult.
Once you get familiar with the timing and how the circle bounces, it’ll get easier to control these aspects. And once you’ve got this control, you can collect and break all the diamonds you want (and last longer in the game). Happy diamond breaking!