Calcium Carbonate
Calcium carbonate crystals usually appear as large yellow-brown or colorless spheroids with radial striations. They can also be seen as smaller crystals with round, ovoid, or dumbbell shapes.

These crystals are common in the urine of normal horses, rabbits, guinea pigs and goats. They have not been observed in canine or feline urines.
Calcium carbonate crystals in urine from a horse. Classic forms are round in shape with radial striations and are yellow brown (arrows). Several other variants (ovoid, dumbbell) are also seen in the background.
 
© Cornell University