Kidney stones are little crystals that form into pebble-like stones in the kidneys. Some may block the urinary tract. What kidney stones look like can depend on what they consist of. The appearance can vary in size and color.

This article will discuss what kidney stones are, what causes them, their symptoms, treatments, and prevention.

According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), kidney stones form in the kidneys due to high levels of certain substances, such as calcium, in the urine.

Kidney stones can vary in size and can be smooth or jagged. They are usually brown or yellow.

There are four main types of kidney stones.

Calcium stones

One 2016 article states that calcium stones are the most common type of kidney stones.

Calcium stones contain calcium oxalate, calcium phosphate, or a combination of the two.

Calcium oxalate stones consist of calcium oxalate dihydrate (COD), and calcium oxalate monohydrate (COM).

A kidney stone made out of calcium oxalate with COD crystals will have jagged edges. However, a kidney stone formed out of calcium oxalate with COM crystals, which is more common, will have a smooth surface.
Another crystal, brushite, forms little rosettes of very thin, sharp crystals.

Another crystal, brushite, forms little rosettes of very thin, sharp, crystals.

Uric acid stones

According to a 2018 article, uric acid stones account for 3–10% of kidney stones.

Uric acid stones are usually pebble-like in appearance. Some of these stones may be hard on the outside, but softer on the inside as they consist of different types of uric acid and calcium oxalate monohydrate.

Struvite stones

Struvite stones are the next most common type of kidney stones, with 7–8% of people worldwide having them.

These stones are larger than others.

Cystine stones

Cystine stones are the result of cystinuria, which is a condition that can pass down through families.

Kidneys produce cystine, a type of amino acid, and in people with cystinuria, this amino acid leaks through the kidneys and into the urine.

Cystine stones are compact, partially opaque, and are amber.

Symptoms of kidney stones include:

  • sharp pains in the back, side, lower stomach, and groin
  • pink, red, or brown blood in the urine
  • a constant need to urinate, and pain while urinating
  • being unable to urinate, or only urinate a small amount
  • urine that is cloudy or smells
  • nausea
  • vomiting
  • fever
  • chills

The kidney usually filters out waste chemicals in urine, such as calcium and phosphate. However, sometimes the kidney is not able to filter these waste products out.

According to the National Kidney Foundation, this can happen when there is too much waste and not enough liquid in the kidney, causing crystals to form.

Once these crystals form into kidney stones, the stones may stay in the kidney or travel down the urinary tract.

However, sometimes people cannot pass these stones, which causes a back up of urine in the body, causing pain.

People may be able to pass kidney stones without medical treatment.

According to the Urology Care Foundation, smaller stones are more likely to pass than larger stones, as they are less likely to block the urinary tract.

People can wait up to 6 weeks for a stone to pass. A person should drink plenty of water.

People are likely to experience pain when passing a kidney stone. If the pain is unbearable, people should see a doctor.

The doctor may prescribe stronger pain relief medication, anti-nausea drugs, or a medicine called tamsulosin. Tamsulosin relaxes the ureter, a part of the urinary tract, making it easier for people to pass the kidney stone.

A doctor may ask a person to use a device to catch the kidney stones, so they can identify what type of kidney stone it is and recommend treatment.

Passing stones depending on size

According to one article, the average size of a ureter is 3–4 millimeters (mm) wide.

A person’s chances of passing kidney stones depends on its size:

Stone size (mm)How many pass (%)
Less than 480
More than 620

If a person has large kidney stones or stones that block the urinary tract, a doctor may recommend surgical removal.

When people have their kidney stones removed, a urologist, a medical professional specializing in surgeries of this nature, removes the kidney stones or breaks them into small pieces.

There are three types of surgery:

  • Shock wave lithotripsy: This breaks the kidney stones into smaller pieces, allowing them to pass through the urinary tract.
  • Cystoscopy and ureteroscopy: These procedures use a camera to find the stones in the urethra or the bladder. Once the urologist finds the kidney stones, they can remove them entirely or break them into little pieces, which people can then pass through their urine.
  • Percutaneous nephrolithotomy: A urologist will insert a camera directly into the kidney through the back to remove the stones. If the stones are very large, the urologist may use a laser to break them apart.

A person can help do the following to help prevent kidney stones:

Stay hydrated

The NIDDK recommend that people drink six to eight 8-ounce glasses of water a day unless they have kidney failure.

While it is best to drink water to dilute urine, citrus drinks, such as orange juice and lemonade, can protect against kidney stones. This is because they contain citrate, which stops crystals from forming into kidney stones.

Take medication

The table below describes which medication a doctor may prescribe for which kind of kidney stone.

Type of kidney stoneMedication
Calcium stonesPotassium citrate

Uric acid stonesAllopurinol

Potassium citrate
Struvite stonesAntibiotics

Acetohydroxamic acid
Cystine stonesMercaptopropionyl glycine

Potassium citrate


If a person knows what kind of kidney stones they had previously, the following nutrition tips may help prevent them from coming back.

Type of kidney stoneNutrition advice
Calcium oxalate stonesreduce the intake of oxalates, such as nuts and nut products, legumes, rhubarb, spinach, and wheat bran

reduce the intake of sodium

limit animal protein, such as dairy products, eggs, fish, and meat
Calcium phosphate stonesreduce the intake of sodium

limit animal protein, such as dairy products, eggs, fish, and meat

limit legumes, soy foods, nuts, and sunflower seeds
Uric acid stoneslimit animal protein, such as dairy products, eggs, fish, and meat

limit legumes, soy foods, nuts, and sunflower seeds

eat a healthful diet and increase physical activity if a person has obesity
Cystine stonesstay hydrated

Avoid sugary and caffeinated drinks

According to a 2019 study, caffeinated drinks, especially coffee, increase the risk of recurring kidney stones.

Similarly, drinks that contain a lot of sugar increase the risk of people developing kidney stones.

Some factors that may increase the chance of people forming kidney stones include:

  • not drinking enough water
  • too little or too much exercise
  • having obesity
  • weight loss surgery
  • eating food that contains too much salt or sugar
  • eating or drinking things that contain fructose

Preexisting conditions

People are more likely to develop kidney stones if they have:

  • a urinary tract blockage
  • obesity
  • cystinuria
  • gout
  • reoccurring urinary tract infections
  • cystic kidney disease
  • digestive problems
  • hypercalciuria, an inheritable condition where the urine contains too much calcium
  • hyperoxaluria, a condition where the urine contains too much oxalate
  • hyperparathyroidism, a condition where the body releases too much parathyroid hormone, with extra calcium in the blood
  • hyperuricosuria, a condition where the urine contains too much uric acid
  • renal tubular acidosis, a condition where the kidney does not remove acids into the urine, keeping the acid into the blood


People on the following medications are more likely to develop kidney stones:

  • diuretics, which help the body get rid of excess water
  • calcium-based antacids
  • indinavir, a drug that treats HIV
  • topiramate, an anti-seizure medication

According to the NIDDK, doctors diagnose kidney stones through a medical history, physical exams, and tests.

A doctor may take a urine sample.

Urine and blood tests can let a doctor know which kind of kidney stones a person has.

Doctors may also order an abdominal X-ray or a CT scan.

These tests allow a doctor to see how many kidney stones a person has and how large they are.

It is important to see a doctor if a person experiences symptoms of kidney stones.

According to the NIDDK, if a person does not seek treatment for kidney stones, they might be at risk of:

  • blood in the urine
  • severe pain
  • urinary tract infections and kidney infections
  • loss of kidney function

There are four different kinds of kidney stones, each made up of various chemicals. Each of these kidney stones looks different, and each type may require a different medication to prevent them from coming back.

People can pass kidney stones themselves, but they may need help from a doctor. If a kidney stone gets stuck or is very large, a person may require surgery.