Java Edition:Iron Ore (Item)
Iron ore was added in Classic 0.0.14a but items were not added until Classic 0.25_SURVIVAL_TEST. The item could be obtained up till 0.25_SURVIVAL_TEST_05 after which it began dropping iron blocks instead of iron ore. The item remained unobtainable until Indev when it was obtainable in the Indev Chests and then obtainable in Indev 0.31 20100128 and later by simply mining.
Obtaining
Mining
From Classic 0.0.14a to Classic 0.25_05 Survival Test iron ore could be obtained by mining the block, and did not require any silk touch. This was recontinued in Indev 20100128 until 21w13a (1.17 Snapshot) because between Classic 0.26 Survival Test and Indev 20100125 iron ore dropped blocks of iron.
Classic
From Classic 0.28 to Classic 0.30c iron ore was available in the Classic inventory.
Indev Item Chests
From Indev 20100124-1 to Indev 20100128 new worlds would generate with the Indev House, and inside the house were debug chests. Between Indev 20100124 and Indev 20100125 the chests held items in stacks of 99, while in Indev 20100128 the chests held items in stacks of 100. Iron ore was one of the such items that generated inside the debug chests.
Beta 1.6 Debug Chests
In Beta 1.6 Test Build 3 new worlds would generate with 11 debug chests. Within the debug chests were a wide variety of items most of which were available in there full stacks some were not. Iron ore was one of the such items that generated inside the debug chests, iron ore generated in the 1st and 4th chests from the left in the 15th and 26th slots respectively, in stacks of 64.
1st chest from the left.
4th chest from the left.
Silk Touch
Prior to 21w14a (1.17 Snapshot) iron ore would drop itself when mined, but from 21w14a (1.17 Snapshot) until 24w20a (present), when mining iron ore with a Silk Touch tool the block would drop itself instead of raw iron.