RuneScape Classic Wiki
RuneScape Classic Wiki
The Old School RuneScape Wiki also has an article on Adamantite ore.
The main RuneScape Wiki has an article on: Adamantite ore

Adamantite ore is an item which may be obtained from an adamantite rock by players with level 70 in the mining skill or higher. Doing so grants 90 experience when successful. It can be smelted with six pieces of coal to create an adamantite bar, granting 37.5 smithing experience.

For a list of adamantite rock locations, see adamantite rock locations.

Paladin Chest

Adamantite ore can be thieved at level 72 thieving or higher from the Paladin Chest on the the top of the East Ardougne castle.

Dropping monster

Monster Combat level Quantity Rarity
Blue Dragon 105 1 2Common