Jack o lanterns can be mined with any tool, or without a tool, but hatchets are the quickest.
Jack o lanterns cannot be placed without an object under them, but once placed, will remain even if the object underneath is mined away. When placed, jack o lanterns automatically face the player. Jack o lanterns cannot be placed on transparent objects.
Jack o'lanterns are transparent in their rendering only, which means that they have the attributes that all opaque solid objects have. For example, they can suffocate creatures, and objects attached to another object (such as torches and rails) can be placed on top of them or on their sides.