This should serve as a simple guide to Minecraft Ores for new players. As of the 1.3 update there are 7 official ores in Minecraft. There is also one planned for release in the 1.5 update. The official name for all the ores listed by rarity are:
Coal ore, Iron Ore, Redstone Ore, Gold Ore, Lapis Ore, Diamond Ore and Emerald Ore.Coal Ore
Coal Ore is the most common Minecraft Ore found at any level under the Y Axis of 132. Coal Ore can be mined with any pickaxe and when mined, the ore will drop one piece of Coal. Coal Ore can only be found in the Overworld and Coal is sometimes dropped by certain mobs like the Wither Skeleton.
Coal Ore veins are the only kind that can produce more than 10 Coal Ore blocks per vein as they can sometimes contain more than 32 Coal Ore blocks. Coal Ore can also be mined with a Pickaxe that has the Fortune enchantment or the Silk touch enchantment.Iron Ore
Iron Ore is the second most common Minecraft Ore and is only found below layer 68. Iron Ore can only be mined with either a Stone, Iron or Diamond pickaxe and only drops one ore. When smelted in a furnace, Iron ore will produce one Iron ingot as well as a small amount of EXP. No enchantments are effective on Iron ore.Redstone Ore
Redstone Ore is one of the rarer Minecraft Ores to find because it generates lower underground. Redstone can only be mined with a Iron or Diamond pickaxe and when mined, the ore will drop 4-5 Redstone dust. Redstone dust is used in some items and circuits in Minecraft. Redstone veins from from 1-10 blocks. enchantments such as Fortune and Silk Touch can be used on Redstone Ore. Redstone generates at the bottom 14 layers of the map.Gold Ore
Gold Ore, also known as butter, is a rare Minecraft Ore that can only be found beneath the layer 34 and spawns slightly less than Lapis Lazuli Ore. Minecraft follows the realistic portrayal of Gold meaning that it is very weak when used as tools or armor but is faster (somehow) than all other materials. Some Minecraft servers also use Gold as a currency. Gold Ore can only be mined with an Iron pickaxe or a Diamond pickaxe and when mined, the ore drops one Gold Ore block which can be smelted in a furnace to produce Gold Ingots. Zombie pigmen drop Gold nuggets which can be crafted into Gold ingots.Lapis Ore
Lapis Lazuli ore is one of the most rare Minecraft ores to find. It spawns less than Gold ore does and is known for being practically useless other than for decorations. This is where the name "Useless Lazuli" comes from. Lapis Lazuli ore only spawns below the layer 33 making it hard to find. Lapis Lazuli ore can be mined with a stone, iron or diamond pickaxe and when mined, the ore drops multiple Lapis lazuli. The Fortune enchantment and the Silk Touch enchantment can be used on Lapis Lazuli ore.Diamond Ore
Diamond Ore was at one point the rarest Minecraft Ore there was. It spawns only at layer 16 and below and is only obtained using an Iron pickaxe. Diamond Ore is very rare and is used to make the strongest tools and armor. It is hypothesized but not proven that diamonds spawn more wherever there are lava lakes under the level 16. When mined, Diamond Ores will drop a Diamond. Because of they're rareness, there are several jokes surrounding Diamonds like "Creepers only appear when diamonds are near." Both Fortune and Silk Touch can be used on Diamond Ore blocks.Emerald Ore
Emerald Ores are now the rarest Minecraft Ores of all as of the 1.3 update. Emerald Ores only spawn in veins of 1 Ore block beneath the layer 33. Emerald Ores also only spawn in Extreme hills biome. Emeralds are much rarer than Diamonds and are used only to trade with villager npcs for sometimes normally unobtainable items.
Hopefully this guide will be helpful to guide you through all the various Minecraft Ores. This guide will be updated as more ores are added. For more information about the different types of minecraft blocks check out this area