From Nookipedia, the Animal Crossing wiki
Every day, a Money Rock, also known as a Bell Rock, will randomly appear around town and spurt out Bells after being hit with a shovel or an axe. The rock can be hit repeatedly for increasing amounts of money although the allotted time window for a hit to produce money decreases after each hit. In all versions, every bag spouted after the fourth consecutive bag/coin will play the '1-Up' noise from the Mario series.
The amount of money the rock gives varies from game to game and depends on how fast it is hit, the level of yellow Feng Shui, and, in Animal Crossing: City Folk, what it is hit with. Any obstacle adjacent to the money rock will also prevent bags from spawning there. For towns with more than one player, each player gets the money rock from separate random rocks.
In Animal Crossing
In Animal Crossing, the rock will spurt out up to 23,300 Bells as three sacks of 100, three sacks of 1,000, and two sacks of 10,000. Having high levels of any (not just yellow) feng shui will increase the chance of more money spouting from the rock. Also, the money rock glows red when hit and gradually fades to gray, giving a visual timer as it will continue to spout money for as long as the rock is red. In later versions the rock simply remains gray.
In Wild World
In Animal Crossing: Wild World, the rock in the player's town will release up to 8,500 Bells as sacks of 100, 200, 400, 800, 1,000, 2,000, 4,000 Bells, in that order. High levels of yellow feng shui may allow for an additional 8,000 Bell bag to appear.
In City Folk
In Animal Crossing: City Folk, the money that comes out is different. The order goes: 100, 200, 300, 500, 1,000, 2,000 and finally 4,000. If the player uses a silver shovel, one of the money bags may double, with a signature noise and sparkle; it has a 10% chance of happening. It has been proven that high yellow feng shui (over 73 yellow feng shui count) means that an 8,000 Bells bag will appear. If the two are combined, that's up to 10,100 Bells. Having a silver shovel equipped will cause twice the amount of money to pop out 10% of the time.
In New Leaf
In Animal Crossing: New Leaf, if the money rock is struck with an ordinary shovel, players can receive up to 16,100 Bells, with a 0% chance of receiving ore. With the silver or golden shovel, players can receive up to 32,000 Bells and there is a rare chance an ore appears instead of the daily money.
After every hit against the rock, the player will rebound, causing the player to lose time and making it impossible to collect all of the potential money sacks. To prevent this, players can dig holes behind themselves to create a wall to prevent getting knocked back too far. Examples are shown below.
Natural features, such as trees and cliffs, if close enough, can also be used to prevent kickback, taking place of one or more holes.
Money per year
The money rock appears once every day. If the rock is stricken enough times every day, players can make this amount per year:
or, in a leap year: