Quick way to get earth crystals?

[niko]

I need to make a lot of mayo machines but finding earth crystals is a challenge.

[Omegatherion]

Best chances is between level 10 and 30 in the mines.

[Pixel Peeper]

They're fairly common in the "earth" type floors in the Mines. Half a day of running through those levels real quick should yield many of them.

Duggies also drop them sometimes. They're also found in ordinary Geodes, but it's rare.