Java Edition:Cobblestone
The cobblestone block was discontinued in several classic versions during the early development of Minecraft.
Obtaining
The cobblestone block was first obtainable in pre-Classic rd-160052 when different block IDs were added to the game. The cobblestone textured block in earlier version has the ID 1 and will convert into stone when updated.
First Discontinuation
In Classic 0.0.19a, Notch added the hotbar to the game. There was not enough room for all the blocks and so he left cobblestone and sand off the hotbar. Cobblestone does not naturally generate in the world and so there is no way to obtain the block until the inventory is added in Classic 0.0.20a (Classic 0.0.20a_01 is the first archived version after Classic 0.0.20a, which is missing).
Second Discontinuation
Starting in Classic 0.24_SURVIVAL_TEST the player was put into survival mode and lost access to the creative hotbar. Cobblestone doesn't generate in the world so there was no way to obtain cobblestone along with other blocks formerly obtainable in the creative inventory such as cloth, sponge, and glass. Cobblestone became obtainable again in Classic 0.26 SURVIVAL TEST (Classic 0.27 SURVIVAL TEST is the first archived version after Classic 0.26 SURVIVAL TEST, which is missing) when stone, which does generate in the world, began to drop cobblestone when mined. This change made the stone item discontinued. The cobblestone block was obtainable in Late Creative Classic from the creative inventory again and then has been obtainable in survival mode ever since.
See also