|Source Mod||Vanilla Minecraft|
Glowstone is an ore found in the Nether or in Mystcraft Ages written with the Glowstone feature. It is typically found growing from the roof of the Nether in coral-like formations. Glowstone drops 1 to 4 glowstone dust when mined by hand. It can also be mined with a Rock Cutter or another tool with the Silk Touch enchantment to gather the block, which can then be infinitely processed back and forth in a Macerator to turn it to dust and a Compressor to turn it back to blocks without any loss of Glowstone Dust. However, this requires some sort of method of EU generation.
Using a Jetpack or an Electric Jetpack can make the collection process of glowstone easier. Also useful are a Rockcutter/Silk Touch tool for gathering the blocks themselves, a Portal Gun (as portals can be placed on Glowstone itself, despite it being a technically "transparent" block) and some way of defending oneself from Ghast fireballs, as mining Glowstone can leave the player in a position which is very vulnerable to Ghast fire.
For more information, see this item's Minecraft Wiki page.