Tin Mine

Age of Empires III does not have gold as a resource, but instead has coin, an amalgam of all forms of wealth.

Appearence
One of the many sources of coin can be found in Tin Mines, a rare mine. It is the most quickly expendable source of coin in the game, and has been introduced in the WarChiefs expansion.

They don't appear exclusively in a map, but are randomly added in maps introduced after the WarChiefs expansion, along with other mines. Oddly enough, they are identical to appearence to Silver Mines.

Mining
Tin Mines provide which can be mined by Settlers and Villagers, as well as Miners.

Settlers can gather coin faster from the Tin Mine with Market upgrades such as Placer Mines and Amalgamation.

History
"As in the case of copper, people have gathered and mined tin for thousands of years. It key value to the ancient world was in combination with copper, the creation of bronze - an alloy widely used for weaponry and art. Because of its ability to inhibit corrosion, tin has long been used to coat steel and other metals. Indeed, the commonly referred to "tin can" is actually made from steel, with only a minimal tin plating. Even though scarce, tin is found all over the world and on every continent. Most tin processed today is mined in Southeast Asia."

Trivia

 * Ironically, while tin is the rarest mineral in Age of Empires III, it is also the least valuable.