The monsters are going green! To preserve the natural beauty of their world, the monsters have decided to replace the existing mine structure with a smaller one that is friendlier to the environment. Even though it produces diamonds a little less often than its predecessor, the monsters are proud of their decision and always recall that good things come to those who wait.
The mini-mine is a Structure that provides 1 Diamond every twenty-four hours. This is a much slower rate than the regular Mine, but it can be purchased with coins instead of diamonds. Only one mine (mini or regular) may be built on an island, but each island can have its own mine. The mini-mine was introduced with the update to version 1.1.3 and permanently replaced the regular mine on 1 March 2013.
The mini-mine used to start with 1 diamond after purchase, but no longer does that.
The predecessor cost 20 diamonds and produced 2 diamonds/12 hours.
In the update 1.3.0, updated in about 7th October 2014, the original Mine, now called the Maximum Mine, made a comeback on Plant Island, but it is only upgradable or buyable in the Market if you buy at least one pack that costs real money.
When all Mines have obtained some diamonds, they used to present an actual unit of diamond in their cave. In a later update, the mines have their ready-to-collect diamonds onto their crate or cart.