Why is Whale vomit so valuable ?

Because it can change stone to gold. No it can't do this. Actually when whale eats animals like squids they digest most of their body parts.However sharp peaks are indigestible that can cause irritation in digestive track. Thus whale digestive system secrets a waxy substance called Ambergris, which protects the digestive track from sharp peaks, helping them to pass through the track easily.

                Now some people will think that whale vomit this Ambergris through mouth but it's wrong. The expell their Ambergris through the other end(back side) . When this Ambergris react with air ,salty water then it gets into waxy rock. This waxy rock is purchased by perfume companies. Why??

This Ambergris can stick to our skin and smells great for longer. That's why this Ambergris is purchased by various perfume companies at very high rate.