Opalescence is a simple mod that adds Opal, a new stone type that changes hue depending on its location in the world.

Opal generates naturally in the underground. It can be uncommonly found in the deepslate layer below Y=0, or more rarely in the stone layer between Y=32 and Y=56. Some of the naturally generated stone will bear crystals, which can be crafted into regular opal blocks, allowing for a renewable source of opal.

Letting the moon shine on fully grown, but still attached to the budding block crystals lets them aqquire a new, pearlescent hue (doesn't work when moonlight is weak). These moonlit crystals can be crafted into their respective opal variant.

Both regular and moonlit opal can be crafted into various different shapes. Just plop down the stone into a stonecutter (or smelt it) and choose whichever variant you like best :)

(1.0.4+) The opal can be made emissive by right-clicking it with a glow ink sac, or by placing it while holding a glow ink sac in the offhand slot. The glow ink sac will not be consumed :)

You can also make some "interesting" hues by placing a full composter under the budding opal block and letting it influence the grown crystals. Why would you do that though?
Alex's Caves:
Ars Nouveau:
Create:
Farmer's Delight:
Spectrum / Pastel: