MINERALOGY OF KIDNEY STONES

Kidney stones are pathological crystalline build-ups in the human body that are usually minerals identical with those found in nature. A few of the crystalline compounds that may form are organic chemicals, like cystine (an amino acid) and uric acid. Most gall stones are also crystallized organic material, usually cholesterol. The exact cause of all kidney stones is not well understood, but factors probably include genetics, diet, and disease.

Dick Gibson's first career was as an analyst of kidney stones and other biological mineral concretions. He examined more than 20,000 of them in 4 years.

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Herewith is a list of common minerals found in stones.

Apatite | Whewellite | Weddellite | Struvite | Brushite | Whitlockite | Newberyite | Others

APATITE is a common mineral in nature. Chemically it is a complex calcium phosphate with attached molecules of hydroxyl (OH), fluorine (F), and sometimes, other elements. Apatite is the fundamental mineral component in bones and teeth, and when apatite has fluorine in its crystal structure, it is stronger. This is why fluorine is added to water and toothpaste. In kidney stones, carbonate (CO₃) substitutes for some of the phosphate, making a mineral that is relatively poorly crystallized. Its formula in kidney stones is usually given as Ca₅(PO₄,CO₃)₃(F, OH, Cl). Well-crystallized or not, apatite often forms the nucleus upon which other urinary minerals are deposited. It usually occurs as a white powdery mineral deposit. Mineral Name Index

WHEWELLITE

WHEWELLITE is a calcium oxalate (CaC₂O₄^.H₂O) that is extremely rare in nature. It is known to occur in septarian nodules from marine shale near Havre, Montana, with golden calcite at Custer, South Dakota, and as a fault filling with celestite near Moab, Utah. It is found in hydrothermal veins with calcite and silver in Europe, and it often occurs in association with carbonaceous materials like coal, particularly in Saxony, [former] Czechoslovakia, and Alsace. It is one of the most common kidney stone minerals, however, where it typically occurs as small, smooth, botryoidal to globular yellow-green to brown, radially fibrous crystals. Whewellite stones larger than ½ inch across are quite unusual. Often whewellite is deposited upon a tiny nucleus of apatite, which may form as build-ups on the tips of tiny papillae in the kidney.

WEDDELLITE

WEDDELLITE, CaC₂O₄^.2H₂O, was named for occurrences of millimeter-sized crystals found in bottom sediments of the Weddell Sea, off Antarctica. Unfortunately the sharp yellow crystals that urinary weddellite forms are often much larger than that, and they are frequently the cause of the pain experienced in passing a kidney stone. Rarely, weddellite crystals may occur that are neary a half inch on an edge, but most are somewhat smaller. The yellow crystals are commonly deposited upon the outer surface of a smooth whewellite stone. Like whewellite, weddellite is a calcium oxalate. They differ in the amount of water that is included in their crystal structures, and this gives them very different crystal habits. Occasionally, weddellite partially dehydrates to whewellite, forming excellent pseudomorphs of grainy whewellite after weddellite's short tetragonal dipyramids. Together, apatite, whewellite, and weddellite are probably the most common urinary stones.

STRUVITE is a magnesium ammonium phosphate, Mg(NH₄)(PO₄)^.6H₂O, that forms distinctive coffin-shaped crystals. Often masses of tiny crystals grow together with powdery apatite to form huge branching stones called "staghorns," which may be several inches long. They may even fill up the entire open area of a kidney. Struvite stones are sometimes associated with bacterial infections of the urinary system. They also require non-acid systems to form, as indicated by the presence of ammonium (a basic, non-acidic compound) in the crystalline structure. The only common occurrence of struvite outside the urinary system is in bat guano. Certain dogs (especially dalmatians) can produce remarkable large, smooth, milky-white tetrahedrons of well-crystallized struvite.

BRUSHITE

BRUSHITE is a calcium phosphate compound, CaHPO₄^.2H₂O that is very similar to the common mineral gypsum (Calcium Sulfate). Gypsum finds its greatest use in sheetrock and other wallboards used in home construction. Brushite is a rare mineral outside the urinary tract, and even there it probably occurs in fewer than 10% of all stones. It is a soft, silky mineral, usually honey-brown and showing a fine radial fibrous structure. It can only crystallize in a limited range of pH (acidity), so treatment may include changing the acid-base balance of people who make brushite kidney stones.

WHITLOCKITE is very rarely found in the urinary system, but it is the most common mineral found in prostate stones. It is a calcium phosphate with small amounts of magnesium, Ca₉(Mg,Fe)H(PO₄)₇, and its occurrence may be stabilized by trace amounts of zinc. Prostate fluid has a very high zinc content. The mineral is a resinous, brown, hackly-fracturing material, and it commonly forms multiple small stones in the prostate.

NEWBERYITE is an acid Magnesium Phosphate, MgHPO₄^.3H₂O (unlike struvite, which contains ammonium) that is rare in kidney stones. When it does occur, it often occurs as tiny isolated globular crystals on the surfaces of apatite-struvite stones. This probably reflects an alteration of struvite to newberyite, or perhaps a change of conditions to more acidic solutions. Newberyite may be associated with infections of the bacterium Proteus.

Some of the other minerals that occur extremely rarely in kidney stones include monetite (calcium phosphate), calcite (calcium carbonate), aragonite (calcium carbonate), and hannayite (magnesium phosphate).