Taking a break from literal gem dice to show off the best d4s ever made. Not only are these not caltrops waiting to pierce slippered feet at night when a stray one happens to be right where you're stepping in a rapid trip to the bathroom after a night of drinking way too much tea while playing RPGs, they also roll much better.
Whoever invented these is a genius.
My wife has one of these from a dice set and I love it. I tried to buy myself a couple of them from my local board game store but they don't have them...
They're called Arch'd4¹ and can be found in various online venues if your local purveyor won't stock them.
¹Link is representative. I'm not recommending this particular site because I can't buy from any western source.
I think we've been calling them 'pill' d4s over here.
I even made some wooden ones before they started selling them at my flgs.