Over 20 years ago I pulled my first set of platinum spark plugs out of a car because the engine was missing badly. Two of the six plugs each had one whisker in the gap between electrodes. One crossed the gap and one was most of the way across. They started on the platinum center electrode and grew to the Inconel side (ground) electrode. They looked like straight, fine threads.
As I had worked in metallurgical R&D most of my life, I assumed they were whiskers, odd but no big deal, threw them away and put in new regular plugs. I was retired or I could have had a much better story with XRD and electron microscope data.
The reason I ask is that today I looked up metal whiskers in Wikipedia and found mostly info on whiskers formed on various solders and nothing on platinum.