Those are crystals of the various salts in the urine.
When any solution (something dissolved in water or other liquid) cools off (after leaving your body), some of the dissolved salts turn into visible crystals. There is no problem or health hazard there. If you want to learn about how crystals work in general, try dissolving lots of salt in hot water. When it cools, all sorts of crystals will form, since there's too much salt to stay dissolved.
That is what your diamond-shaped crystals are. They are the salts that your body is getting rid of in a normal way through your urine, becoming visible when the urine cools.
Hello,
If you having such symptoms then the first possibility that needs to be ruled out is of kidney stones.They can be as small as sand particles and can pass through the urine.
I sincerely suggest you to get an examination done by a surgeon/urologist and investigations like urine examination and ultrasound lower abdomen done to confirm the diagnosis.
Hope it helps.Take care and please do keep me posted.