MeteorCraft

Meteorcraft is a mod which adds meteors in the form of balls of different ores and depending on which type of meteorite stone/netherrack/endstone.

Meteorites
Stone Meteors have a 71% chance of spawning and can only contain ores that are found in the overworld. Netherrack Meteors have a 19% chance of spawning and can only contain ores that are found in the nether. Endstone Meteors have a 10% chance of spawning and can only contain ores that are found in the end.
 * Stone Meteors (71%)
 * Netherrack Meteors (19%)
 * Endstone Meteors (10%)

By default 40% of a meteorite is ore and the rest is depending on the type of meteorite stone/netherrack or endstone.

More info can be found here.