Head for the Purple Islands for today's Geo Quiz.

The "Iles Purpuraires" or Purple Islands lie in the blue Atlantic... just off the coast of a North African country we want you to identify. The islands actually get their name from a snail. It's a tiny snail that played a big role in ancient history.

Purple Islands

But -- try telling that to some local fishermen in the port city Essaouira and you may get a confused look:

(Simon Winchester) This snail is the most important thing that Essaouira ever produced. What is it? (Local fisherman) They call it "sha sha." (Winchester) You may know that 3000 years ago, these were worth their weight in gold! (General laughter)

Don't laugh! Author Simon Winchester insists this tiny snail made a lasting contribution to world history. He explains how --- and reveals the name of the North African country.