The Minewood Core is the functional block of a Miner's Tree, one of the four magic trees introduced by the Twilight Forest mod. This block can be activated or deactivated with a right click. When active (i.e. when the gem embedded in the trunk is green), it will draw in nearby ores (note that "ores" include oreberry-bushes, infused stone blocks and amber-bearing stone if playing with Thaumcraft 3, and sometimes just plain stone blocks) with a radius of approximately two chunks. (verification needed) Whether active or inactive, it gives off light with a level of fourteen, the brightness of a torch.
It can be broken and obtained only by using a silk touch tool which is NOT an axe. If you use an axe, TreeCapitator will be invoked, and the axe's silk touch enchantment will be disregarded.
If you place it by yourself, it will still work so if you wish to move your miner's tree, just mine out the Minewood Core and it'll work with just that.