Gemcorns



Gemcorns are a type of seed whose saplings grow into Gem Trees, and can be crafted from an Acorn and any Gem. Natural Gem Trees can be found in the Underground and Cavern layer, although they are rare. Generally speaking, chopping down a Gem Tree will yield 7-48 Stone Blocks, 0-11 Gemcorns of the tree's type, and 0-24 Gems of the tree's type (each tile of the tree has a chance of dropping a gem, otherwise dropping 1-2 Stone Blocks, and every non-barren leaf/branch tile additionally has a  chance to drop another Gemcorn. See Growth section for detailed info.)

Farming


The minimum requirements for a Gem Tree to grow is for it to be planted on one of two immediately adjacent Stone, Moss, or any of their biome variants at the Underground or Cavern layer, displayed by the Depth Meter. Light levels do not affect the growth of Gemcorns at all, therefore light sources can be placed nearby to help the player see better. However, placed torches will prevent tree growth, so do not place any torches within two tiles to the left and right of the sapling. Once a sapling is placed, it cannot be picked back up.

Background Walls
To reduce enemy spawning in a Gem Tree farm, it is possible to place background walls in almost all of the background, except the two tiles occupied by the placed Gemcorn. Some underground enemies (and critters) will still spawn, but far fewer than with an un-walled farm.

Gemcorns can grow in front of fences like other trees. They can also grow in front of natural walls. Of course, natural walls will allow enemy spawning as usual.

Spacing
The Gemcorns must be planted with three tiles of space between saplings for both to be able to grow.

Gemcorn saplings need at least 11 blocks of open space above them, but 16 is better, and 17 will avoid the topmost leaves clipping into the ceiling. The tree size is determined every time the sapling attempts to grow, and if there are fewer than 16 blocks the attempt might fail. Thus, having fewer than 16 blocks available will effectively slow down growth, and will produce only shorter trees (which will yield fewer gems).

Growth
Gem trees can be 7-12 tiles high (not counting space taken up by the non-tile "leaves" at the top) consisting of 6-11 "trunk" tiles topped by one "leaf" tile, with up to 2 additional "trunk" tiles at either side at the bottom, and 0-10 (depending on tree height) "branch" tiles off of the trunk (one tile per branch), totaling between 6-13 "trunk" tiles, 1 "leaf" tile, and 0-10 "branch" tiles. "Trunk", "leaf", and "branch" tiles drop either 1 Gem (10% chance) or 1-2 Stone Blocks (remaining 90% chance). "Leaf" and "branch" tiles also drop 1 Gemcorn 50% of the time if the leaf/branch tile is not barren (barren branches/leaves are fully colored stony gray, containing no visible "gem leaves"). If they are barren, they will drop nothing. Incidentally, branches have a chance to be barren, and leaves have a  chance to be barren.

Tips

 * Using different-colored gem torches or Gemspark Blocks beneath each sapling can be a good way to indicate which type of tree is planted where. Alternatively, paint can be used on the other blocks (as in the picture above); a Gemcorn planted on a painted block will sprout into a painted Gem Tree (just as it would with other types of trees) that could instead make it difficult to see the type of gem due to the coloring.
 * However, using the Illuminant Paint on the actual blocks where Gem Trees are planted could help to tell the gems apart, since it causes the trees and the colored gems on it be fully visible, regardless of lighting (or lack thereof).
 * Gem Trees will grow faster when placed further apart, but times will still vary.
 * Gemcorns can be sold for the value of their respective gem.
 * While Diamond and Amber sell for the highest price directly, any gem except Diamond can be crafted into Stained Glass worth, requiring 5 blocks of Glass.
 * While Gemcorns can be planted on mossy stone, the outgrowths of moss can block the sapling's growth. Furthermore, while a single stroke of a pickaxe will normally remove moss from Stone, this does not work if a Gem Tree has grown on the block. (Moss can still be removed from beneath a sapling)
 * The required empty 3 adjacent Stone Blocks to where the sapling will be planted can be hammered to eliminate waste via accidentally planting Gemcorns too close together as they cannot be planted on hammered blocks. The Smart Cursor function can also be used to avoid this.
 * Gemcorns cannot be placed in a space occupied by water. If water is placed after the Gemcorn is planted, it will not grow.
 * *(verify please) Gemcorns will not grow in the underground desert (at least on console)