Urine crystals can occur for a variety of reasons, many harmless. Here are the different types and how they’re treated. ... Hippuric acid crystals are often found clustered together.

The reason is because cat urine contains uric acid crystals and these aren't water-soluble. This makes cat urine one of the most difficult liquids to remove with regular cleaning methods.

Later in the 19th century, von Liebig’s last student, Oscar Loew, also studied hippuric acid. In 1879, Loew wrote about the source of the acid in herbivores’ urine. According to an account of the ...