It is protein, thickened gallbladder mucoprotein with tiny entrapped cholesterol crystals.
I believe you are talking about Gallbladder sludge.
Antibiotic "ceftriaxone" can also precipitate in the gallbladder and bile ducts as sludge.
Gallbladder sludge, or thickened gallbladder mucoprotein with tiny entrapped cholesterol crystals, is thought to be the usual precursor of gallstones. Sludge may also occur in asymptomatic patients with prolonged fasting and can be seen on standard ultrasonography of the gallbladder. Sludge can sometimes cause biliary pain, cholecystitis, or acute pancreatitis. The Antibiotic "ceftriaxone" can precipitate in the gallbladder and bile ducts as sludge.