Correct syntax for Bitcoin URI: bitcoin://1xxx-etc or bitcoin:1xxx-etc? To make clickable Bitcoin links, to let people easily pay from their wallet, I see two formats being used in various situations:

bitcoin:14bTZTm1uX2uVAqHr62oyGFEkwy2mNLbVb?amount=0.25
and 
bitcoin://14bTZTm1uX2uVAqHr62oyGFEkwy2mNLbVb?amount=0.25

So that's with and without the two slashes. When testing on Android, they both seem to work. Which is correct?
The correct format is bitcoin:&lt;address&gt; as defined in BIP21 and extended in BIP72.

The format with the slashes is mimicry of the HTTP URL format.  Tim Berners-Lee has apologized for inflicting those extra slashes on the world. :-)