Grow ores like sugarcane!
Ore reeds allow you to get ores renewably, without endless mining. They can't grow on just any old block, but must be planted on ore essence (the black one) or gem essence (the white one). They also need to be planted next to lava to get all the nutrients they need to grow. Diamonds, emeralds, lapis, gold, ender pearls, and blaze rods are all planted on gem essence. Coal, iron, redstone, nether quartz, glowstone, obsidian and clay can all grow on either ore essence or gem essence. An ore reed takes on average 36 minutes to grow, twice as long as sugarcane.
It does take quite a bit of time and resources to set up an ore farm. This is Minecraft after all, so you should expect to have to do some mining in the beginning. The main benefit of the reeds comes in the late game, when you've gotten bored of mining but still need to repair your equipment. It takes a while to grow the ores, so start early.
So how do you make these blocks and reeds?
For the essences, shapeless crafting like so:
Ore essence must be made with coal and not charcoal.
To make the reeds, use shaped crafting like so:
Finally, when you've grown your reeds and want to turn them back into something useful, use these (shaped crafting) patterns:
Diamond, emerald, iron, gold, ender pearls and blaze rods all take 8 reeds to make, in the pattern shown above. Coal, lapis, obsidian, and nether quartz need 4, and redstone, glowstone dust, and a clay ball can each be crafted from a single reed.
If you want a similar but easier mod, consider Ore Canes instead.
This mod was inspired by B0bGary's Growable Ores, which sadly was never updated past 1.7.