@dr.hatoo: Bilirubin crystals are seen in the urine when the serum bilirubin level is increased. The macroscopic appearance of urine with bilirubin crystals is orange to almost black in color. The crystals themselves appear as gold-orange needle-like forms that are sometimes clumped together. Hematoidin has a golden-brown crystalline pigmentation and is composed of thread-like filaments arranged in star-shaped clusters akin to a Medusa's head. Hematoidin forms when erythrocyte extravasation occurs in a closed tissue compartment and is a result of hemoglobin metabolism under low oxygen tension conditions.