The tile that drops the Heart of Thorns is a 2x2 tile that is placed once during world generation. It can spawn between 100 and 600 tiles horizontally of the World Spawn Point in either direction on a flat pair of normal Grass Blocks.
Surrounding this object are several 1x1 decorative Thorn tiles. Similar to Strange Plants, they visually appear to be bigger than they actually are, and like Cobwebs, they can be destroyed just by the hitbox of a tool or weapon touching them.
These decorative blocks can only spawn within 20 tiles horizontally on either side of the Heart of Thorns, but can vertically spawn anywhere within the Surface layer.