The sapphires can be found in large clusters along the caverns of BFD

Horde Faction Quests: Allegiance to the Old Gods - Bring the Damp Note to Je'neu Sancrea in Ashen-vale. The Damp note drops seven souls gold from a random Black-fathom Tide Priestess somewhere in BFD before the instance portal.

Allegiance to the Old Gods - Part 2 - Return to the Black-fathom Deeps, find and kill Lorgus Jett.

Lorgus Jett is located near the end of the BFD instance.

Trouble in the Deeps - Visit Je'neu Sancrea in Ashen-vale, he is in need of aid in the BFD. While not a quest in BFD, this quest leads you to BFD as a Horde player and is a prerequisite for The Essence of Aku'Mai quest.

The Essence of Aku'Mai - Bring 20 sapphires of Aku'Mai to Je'nea Sancrea. The sapphires can be found in large clusters along the caverns of BFD before the instance portal.

Dual Faction Quests: Black-fathom Villainy - Kill the Twilight Lord Kelris and take his head to the correct faction NPC listed above.

Of course, there is less WoW gold and experience (WoW power leveling) than you have defeated a boss in Black-fathom Deeps. Twilight Lord Kelris is located near the end of the BFDs.