Ores

Ores are primary crafting materials necessary for game progress. They generally must be crafted into bars at a Furnace, after which they can craft several essential tools, weapons, armor, and other items. Some items require raw ores themselves, most commonly bricks and potions. Raw ores can also be used as plain blocks for construction.

Ores are generally found as veins of placed blocks in the Underground layer and below, and are mined with a pickaxe or drill. Lower-tier ores can be found among Dirt near the surface, or within Floating Islands. Some ores are also dropped by bosses, namely Eye of Cthulhu, Eater of Worlds, Brain of Cthulhu,, and.

An Extractinator and Wooden Crates (from Fishing) also provide ores as random rewards.

A world will generally only contain one ore type from each tier, which are chosen at random (see tables below). The alternate ore types that do not generate naturally in a world can be obtained from crates, as bonus drops from Slimes, from an Extractinator, or from other worlds. Hardmode ore types are chosen at random when players destroy Altars.

Pre-Hardmode
Note that there is also "Tier 0" equipment: Armor, tools, and weapons made of wood, cactus, or pumpkin.

Hardmode
Spawning the first three tiers of Hardmode Ore requires the destruction of Demon/Crimson Altars. This requires a Hammer with 80% hammer power or higher, e.g. the Pwnhammer.

Chlorophyte Ore spawns on its own once Hardmode is triggered, and Luminite does not occur naturally. Neither are affected by destroyed Altars.

Tips

 * Each Hardmode ore is chosen at the moment the first three Altars in the world are broken. Ores can be "chosen" by quitting the world without saving (by ending the task or killing the process) after smashing the first Altars. It is more easily done with a server, using the  command.
 * All ores except Hellstone and Obsidian are highlighted by the Spelunker buff, making it easy to find veins of ore. Hellstone is not lit up by the buff, but it is by a Dangersense Potion. Obsidian is easily found and made around lava.
 * Using a Crate Potion will improve the chances of obtaining Crates, and as such the ore-bearing Wooden Crates.
 * Filling in caves with spare natural blocks such as dirt before destroying Altars can cause Hardmode ores to spawn in them. They can then also be seen on the minimap, presenting an easy way to convert extra blocks into ores with knowing their exact location.
 * In the, the Palladium Pickaxe and Drill can mine Adamantite and Titanium.
 * Most ores sell for the same as or more than the bars made from them. The exceptions are the late pre-Hardmode ores (Meteorite, Demonite/Crimtane, Hellstone), and Chlorophyte, all of which are far more profitable as bars. (Hellstone and Obsidian are unsaleable as ores, and there is no Obsidian Bar).

Trivia

 * Hellstone's item sprite is a recolor of that of Silver Ore.
 * Hellstone and Chlorophyte are the only ores that cannot be infinitely generated within a single world. Others can be obtained from sources such as Crates, an Extractinator, bosses, duplicable liquids, and Meteorite crashes. Furthermore, Chlorophyte can be grown using mud, which, while not truly infinite, is unlimited for all practical purposes.
 * Iron and Lead are the only ores not to have bricks.
 * Despite being a late-game ore, Chlorophyte Ore only sells for per ore. This could be because it can be farmed indefinitely, but its bar (and derivative bars) fall right into sequence pricewise.  Luminite sells for the most, netting  per ore.
 * Palladium, Cobalt, and Titanium are the only Hardmode ores named after real metals.
 * As of version, there are a total of 21 types of ores in Terraria.
 * Luminite is the only ore that does not require a Furnace to craft bars.

History
Erze Minerais Ércek 광석 Rudy Ores Руда 矿石