|Gravity?||No, but cannot stay in air.|
A Cactus is one of several naturally-occurring blocks of vegetation in Minecraft. It can only be grown on sand, and can grow to a maximum of 3 blocks tall. If a player or mob touches a cactus, they will begin to take damage as long as they are in contact with the cactus. A cactus will not shear sheep. Any items that come in contact with a cactus will be destroyed. Unlike most plants, Cacti do not need light or water to grow, and are inflammable. Cacti cannot be placed on Sandstone. Blocks touching a cactus block will be destroyed. Blocks can however be placed horizontal to cacti. Cacti are abundant in the Dessert Biome.
Cacti can be stacked as high as the player wants, but can not be found this way in nature. To destroy a large stack of cacti, destroy the bottom block first, the whole stack will collapse.
Cacti are blocks with Opacity. Blocks with Opacity are not "fully complete" blocks or have transparency. For some of these blocks, it may not be possible to place other types of blocks directly onto them. Blocks with Opacity are as follows: Water (Source), Lava (Source), Tall Grass, Oak Sapling, Birch Sapling, Spruce Sapling, Jungle Sapling, Red Mushroom, Brown Mushroom, Red Flower, Dandelion, Crops, Sugar Cane, Cactus, End Portal, Portal, Fire, Sign, Torch, Snow, Air, Enchantment Table, Redstone Torch, Redstone Wire, Button, Pressure Plate, Lever, Rail, Trapdoor, Redstone Repeater, Door, Iron Door, Bed, Cake, Fence, Ladder, Oak Wood Stairs, Spruce Wood Stairs, Jungle Wood Stairs, Birch Wood Stairs, Cobblestone Stairs, Bricks Stairs, Stone Brick Stairs, Nether Brick Stairs, Sandstone Stairs, Quartz Stairs, Stone Slab, Sandstone Slab, Cobblestone Slab, Bricks Slab, Stone Brick Slab, Oak Wood Slab, Jungle Wood Slab, Birch Wood Slab, Spruce Wood Slab, Nether Brick Slab, Quartz Slab, Farmland, Chest, Large Chest, Glowstone, Piston, Sticky Piston, Oak Leaves, Jungle Leaves, Spruce Leaves, Birch Leaves, Glass, and Ice.