Gallbladder stones are hard, pebble-like pieces of material that form inside the gallbladder, and they vary dramatically in color, shape, and size depending on what they’re made of. Most people picture a single round stone, but gallstones can range from a grain of sand to the size of a golf ball, and a single gallbladder can hold just one large stone, hundreds of tiny ones, or a mix of both.
Cholesterol Stones: The Most Common Type
In developed countries, more than 85% of gallstones are cholesterol stones. These are typically yellow-green in color, sometimes with a waxy or slightly greasy surface. They can look like small, smooth pebbles or have a rougher, faceted appearance if multiple stones have been pressing against each other inside the gallbladder for years. Some are pale yellow, almost white, while others lean toward a deeper olive green.
If you were to cut a cholesterol stone in half, you’d see a striking internal pattern. Pure cholesterol stones have crystal structures radiating outward from the center like the spokes of a wheel. Mixed stones, which contain both cholesterol and bile pigment, show alternating light and dark layers arranged in a crescent pattern, almost like tree rings. These layers reflect cycles of material building up over time.
Pigment Stones: Smaller and Darker
Pigment stones form from bilirubin, a substance your liver produces when it breaks down old red blood cells. They come in two varieties: black and brown.
Black pigment stones are small, typically 2 to 5 millimeters across, and rarely larger than 1.5 centimeters. They’re shiny, ranging from dark green to jet black, and often have an irregular, bumpy surface that pathologists compare to a mulberry. Despite their small size, they’re hard enough that you couldn’t crush one between your thumb and forefinger. They also tend to appear in large numbers, so a gallbladder with pigment stones might contain dozens or even hundreds of them clustered together.
Brown pigment stones are softer and crumblier, with an earthy brown color and a greasy texture. They’re more common in parts of Asia and are often associated with infections in the bile ducts rather than the gallbladder itself. When cut open, pigment stones look uniformly dark throughout, without the layered or crystalline patterns seen in cholesterol stones.
How Big Gallstones Can Get
The size range is enormous. The smallest stones are essentially gravel or sludge, just a few millimeters across. Stones larger than 3 centimeters (about 1.2 inches) are classified as “large,” and anything over 5 centimeters (roughly 2 inches) is considered a giant gallstone, though these are rare. For perspective, a 5-centimeter stone would be about the size of a lime and would fill much of the gallbladder on its own.
Size doesn’t always predict symptoms. A single large stone may sit quietly in the gallbladder for years, while a tiny stone can slip into the bile duct opening and cause intense pain. About 15% of the U.S. population has gallstones, and many never know it because the stones never cause problems.
What Gallstones Look Like on Imaging
Most people will never see their gallstones directly. Instead, they’ll see them on an ultrasound or CT scan. On ultrasound, gallstones typically appear as bright white spots inside the gallbladder, with a dark shadow trailing behind them. This is the most reliable way to detect them.
On a CT scan, the picture is more complicated. Only about 20% of gallstones show up as clearly dense, bright objects. Another 30% appear as stones with a visible rim but a less dense center, and 14% show a layered pattern. The remaining stones are either faintly visible or completely invisible on CT. The reason: cholesterol is essentially transparent to CT scanners. The higher a stone’s cholesterol content, the harder it is to see. Calcium-rich stones show up well, but pure cholesterol stones can blend right into the surrounding bile. This is why ultrasound, not CT, is the standard test for suspected gallstones.
When Appearance and Size Matter
Gallstones that aren’t causing symptoms generally don’t need treatment, regardless of how they look or how large they are. Surgery becomes the standard approach when stones start causing problems: repeated episodes of pain in the upper right abdomen, inflammation of the gallbladder, or complications like pancreatitis when a stone blocks the pancreatic duct.
Stone size does play a role in treatment decisions. During procedures to clear stones from the bile duct, stones larger than about 6 millimeters or cases with more than five stones can make removal more technically challenging. Very large stones are also associated with a higher risk of gallbladder cancer over decades, which is one reason some surgeons recommend removal even without classic symptoms in certain patients.
The composition of your stones can also influence what options are available. Cholesterol stones can sometimes be dissolved with oral medication over months to years, though this approach has a high recurrence rate. Pigment stones don’t respond to dissolution therapy. In practice, surgical removal of the gallbladder remains the most definitive solution for stones that are causing trouble.