Lightstone Crystals are incomplete blocks added by Tinkers' Construct. They cannot be crafted nor are they used in any crafting recipes, however they are created through the use of the creative only Glowstone Aggregators. When placed, they give off light similar to Glowstone. They are presently available in 3 styles that resembles Glowstone, Nether Quartz, and a crystallized Lava. Each of the three styles has 4 separate sizes with the first stage appearing to have two separate options for it. In new versions only the white one is available.
On top of a Lightstone Aggregator they can grow up to 3 blocks. If you place a Lightstone more than 1 block high, it can destroy blocks to make room for it.