Just like all the ores in vanilla Minecraft you need a certain level of pickaxe in order to obtain the ore. Here are the levels of all the ores and tools.
Ores:
Stone: Level 1
Copper Ore: Level 1
Tin Ore: Level 1Iron Ore: Level 2
Gold Ore: Level 2
Silver Ore: Level 2
Diamond Ore: Level 3
Blurite Ore: Level 3
Mithril Ore: Level 3
Obsidian: Level 4
Adamant Ore: Level 4
Runite Ore: Level 5
Dragon Ore: Level 5
Tools:
Wooden Pickaxe: Level 1
Stone Pickaxe: Level 2
Gold Pickaxe: Level 2
Bronze Pickaxe: Level 2
Iron Pickaxe: Level 3
Silver Pickaxe: Level 3
Steel Pickaxe: Level 3
Diamond Pickaxe: Level 4
Mithril Pickaxe: Level 4
Adamant Pickaxe: Level 5
Runite Pickaxe: Level 5
Dragon Pickaxe: Level 5