A ruby amulet (u) is made by using a gold bar on a furnace, while having a cut ruby and an amulet mould in the inventory.
Level 50 Crafting is required to make one, giving 85 experience. When used with a Ball of wool, it becomes a ruby amulet, giving 4 experience. The ruby amulet can also be strung using the lunar spell String Jewellery, giving 83 Magic and 4 Crafting experience.
The ruby amulet can then be enchanted into an Amulet of strength through the use of the Lvl-3 Enchant spell, requiring 5 Fire runes, 1 Cosmic rune and level 49 Magic. This gives 59 experience.