No Stone Unturned (Skyrim)

Description
"I've found an unusual gem which seems to exhibit magical properties. I should bring it to Vex at the Thieves Guild for an appraisal. Locations can be found at the page for the unusual gem".

Overview

 * Prerequisite: Taking Care of Business (To the point you meet Vex).
 * Quest Giver: Find an unusual gem.
 * Reward: Prowler’s Profit. (Supposedly an active effect that increases the chance of finding additional gems in chests, but does not appear on active effects list.)
 * Reputation Gain: N/A
 * Bugs: If you're a member of the Thieves Guild and have shown the gem to Vex, when you talk to Maul in Riften about the stone he will suggest becoming a member of the Thieves Guild. A quest objective will be added to join the Thieves Guild; this cannot be cleared.
 * If you've already visited the Thalmor Embassy and missed the gem there, you can jump back to the ledge where you exited with Whirlwind Sprint. (You have to jump from the log onto the edge of the wall, and use Whirlwind Sprint to the ledge. Might require multiple attempts, but it is possible to go back and get the gem.) If someone can provide a video of how to do this, it would be greatly appreciated.

Objectives:

 * 1) Bring the Unusual Gem to Vex in the Thieves Guild. Vex will tell you it is a Stone of Barenziah.
 * 2) Vex then goes on to tell you it is not worth much by itself and tells you that there are 24 of these stones, she will then say if you find them all come back to me.
 * 3) Vex will ask you to recover the Crown of Barenziah from Tolvald's Cave then return to her.

Locations

 * See: Stones of Barenziah