Diamond Ore can be found veins of 1-8 blocks (with larger concentrations being more rare). Diamond shows up at elevations ranging from 1 to 20 blocks above the bottom of the map. Below elevation 18, it occurs in roughly 0.09% of rock.
This can go to approximately 4 diamond ore per chunk.
Mining 771 blocks below elevation 18 has a 50% chance of finding at least one diamond ore.
Diamond, like other ores, is easier to find in caves and empty lava pools, as this gives more surface area.

Gold ore

Gold ore is commonly found by stone blocks deep underground, in a vein of 2-8 blocks (sometimes up to 16 if two veins happen to spawn together, and down to 1 if the block that was supposed to be gold ore is occupied by a cavern or a dungeon). It shows up at elevations ranging from 0 (the bottom of the map) to 35 (about halfway between sea level and the bottom of the map).It can be mined using an iron or diamond pickaxe. Gold ore can be smelted in a furnace to create gold ingots. Tools made with gold will mine much faster than diamond, however because of its very low durability it is more used for showing off than its value on items/armor. It can also be used to create a watch and a powered rail.

Redstone ore
Redstone ore drops 4 - 5 piles of Redstone dust when mined with a Iron Pickaxe or better. Redstone ore forms in veins made up of 1 - 8 blocks. This makes it relatively easy to obtain large amounts of Redstone.

If a player left or right clicks on, or an Entity moves or falls on Redstone ore, the block will emit level 9 light.
Redstone ore veins form at elevations from 1 to 19 meters above the bottom of the map. Below elevation 18, it occurs in about 0.7% of the Stone layer in a map. Redstone ore is commonly found near lava, sometimes in the vicinity of Gold ore or Diamond ore

Iron ore
Iron is a relatively common mineral. It shows up at elevations ranging from 0 (the bottom of the map) to 67 (4 blocks above sea level). It is found in approximately 0.55% of rock below sea level, and falls off sharply in frequency higher up. In Survival Test, it only gave the player an iron block if mined. Most players prefer using iron tools over other types of tools due to Iron's comparative commonness, good durability, and ability to mine almost all of the game's blocks. It was introduced in Creative 0.28.

In Indev, Alpha and Beta, iron ore can be smelted in a furnace to make an iron ingot; iron ingots are used to make all the medium quality tools, armor, buckets, Flint and Steel and shears.
In Beta, iron ore requires a stone, iron, or diamond pickaxe to successfully extract.
Iron ore is often used in player traps as it can be mined and replaced in its raw form.

coal
Coal Ore is a mineral that is a common sight on almost all maps. It is found at almost any elevation, inside caverns, cliff faces, and underground. A lump of coal can be mined directly from Coal ore using a wooden pickaxe or better (that is to say, it is not an ore block so much as it's a vein). Coal lumps can be combined with sticks to make torches, or used as fuel in a furnace or Minecart. When burned in a furnace, it provides 8 uses for each coal lump.

In Survival test, it gave the player 1 to 4 step blocks. It can be placed by players in Creative mode (as of 0.28).
Currently in Minecraft Beta, mining coal yields one lump of coal. Coal blocks are very common to find and are the only ore to appear well above sea level; coal ore comprises about 1% of all rock, regardless of altitude. Common deposits can vary greatly in size - mountaintop deposits are typically limited to five at most, but underground ones can be anywhere between ten and fifty without being noted as unusually large.

Lapis ore

Lapis Lazuli is an ore block that is used to make blue dyes and decorative blocks. Like coal, redstone, and diamond ore, the block yields the resource immediately after mining, requiring no crafting table or smelting. It drops 4-8 blue dye, which can be used to create blue wool, crafted into a Lapis Lazuli block, or mixed with other dyes.
Lapis Lazuli is best mined with a stone or better pickaxe. It is usually found at a depth of 32 and below, similar to Gold. The highest concentration of Lapis Lazuli Ore is found between levels 17 and 19. At this level the concentration is about 0.075%. The concentration drops linearly from this level to 0% at level 0 and level 35. Overall, Lapis Lazuli is around 1.5 times more common than diamond ore.
you know on what level you are by pressing on f3