Money rock

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. The amount of money the rock gives varies from game to game and depends on how fast it's hit, your level of yellow Feng Shui, and in the case of what it's hit with. Anything occupying a space around the money rock will also prevent bags from spouting there. In order to get the most from the money rock the player will need to prevent the kickback from hitting the rock (see below). For towns with more than one player, each player gets their own money rock from a random rock.

In Animal Crossing
In, 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.

In Wild World
In, 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 many allow for an additional 8,000 Bell bag to appear.

In City Folk
In, 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, there's a chance that the money rock will spit out random Gems and Ores instead of Bells when struck with a Silver Shovel.

Preventing Kickback
After every hit against the rock, the player will bounce back, causing the player to lose time and making it impossible to collect all of the potential money sacks. To prevent this, two holes can be dug in positions that will prevent the player from bouncing out of range. While facing the rock, with one hole placed behind the player, another can be placed to either the right or left (see first formation below), or adjacent to the first hole (see second formation below).

Alternatively, the player can stand at a diagonal to the rock, and place two holes in the spaces diagonal to the player (see third formation below). For maximum bell output, each hole should be at least one space away from the rock in order to maximize the number of money bags received, as holes next to the rocks will prevent any money bags from dropping in that spot. For this reason, the third formation can be seen as a safer equivalent of the second.

Natural features, such as trees and cliffs, can also be used to prevent kickback if available, taking place of one or more holes. For this reason, it may also be useful to strategically plant a tree near a rock to reduce the amount of digging required to find and make use of the Money Rock.

Formations
Here are two examples of how kickback can be prevented when striking the rocks. Note that since a maximum of eight sets of bells can drop, the last two formations are often more preferable.

Trivia

 * In Animal Crossing, the money rock will turn red when hit and gradually fade back 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 all versions every bag spouted after the fourth bag/coin will play the '1Up' noise from the Mario series.

Money per year
The money rock appears once every day. If stricken completely every day, players can make this amount per year:
 * 4,854,500 (AC)
 * 3,102,500 (WW)
 * 2,956,500 (CF minimum)
 * 8,796,500 (CF maximum)

or, in a leap year:
 * 4,867,800 (AC)
 * 3,111,000 (WW)
 * 2,964,600 (CF mimimum)
 * 8,820,600 (CF maximum)