Aragonite – One of Two Forms of Calcium Carbonate
Aragonite is essentially a crystalline form of calcium carbonate (CaCO₃), occurring alongside calcite. This means it is calcium in water, which in this case takes the less harmful form of aragonite—though it can also appear as the more damaging calcite in water systems. More on that shortly.
Although both forms—calcite and aragonite—have the same chemical composition (i.e., they consist of the same material), they differ in their crystalline structure and physical properties. Aragonite crystallizes in an orthorhombic system, giving it a different structure than calcite. In nature, it forms in marine organism shells, limestone springs, and mineral deposits. Aragonite is good, and calcite is bad—why?
In hard water, the problem for our plumbing systems is that elements like magnesium and calcium transform into calcite. Calcite is responsible for scale formation—what we know as boiler scale. This is why hard water leads to damage and limescale buildup in water systems and appliances that come into contact with water. Calcite tends to form stubborn deposits that are not easily flushed away. Therefore, calcite is harmful and undesirable.
Aragonite is a powdery form that does not tend to form boiler scale. It is easy to flush out. If water containing aragonite is not flushed (e.g., in closed-loop systems), it will eventually settle as deposits, but these are not hard or solid and can be easily removed.
Precisely because aragonite is more favorable than calcite, some systems install galvanic and silver cells called BlueStream, designed to prevent calcite formation and thus inhibit hard scale buildup. These cells generate a small electric voltage during water flow—typically below 6-7 V—which inhibits calcite formation. Such devices are often mistaken for traditional water softeners, but their operating principle is different and is known as ionic polarization. This water retains the same calcium content, meaning it is technically still hard, but since the calcium takes the form of harmless aragonite that flushes away with the water, it poses no risk.
In water, aragonite can precipitate due to reduced solubility of calcium carbonate, naturally occurring through factors like temperature increases or pressure changes. This is particularly common in heating systems where calcium-rich water is heated to high temperatures. Under such conditions, CaCO₃ precipitates out of the solution, forming crystals—either calcite or aragonite, depending on physicochemical conditions.
The issue is that under natural high-temperature conditions, calcite is favored, so in heating systems, high temperatures primarily promote boiler scale formation—unless the water is soft (i.e., free of hardness-causing minerals). To encourage aragonite formation instead of calcite, we unfortunately cannot rely on basic physicochemical processes and must assist the water with specialized technologies like the aforementioned BlueStream cells.
Compared to calcite, aragonite has a key advantage: it does not form hard, clinging deposits. Its crystals are finer and needle-like, preventing permanent buildup on plumbing components. As a result, aragonite deposits are much easier to flush out and do not cause severe clogging in pipes, valves, or heating elements. This is why many modern water treatment systems intentionally promote aragonite formation over calcite. As a result, household appliances—from showerheads to kettles, coffee makers, and washing machines—experience fewer malfunctions and last longer, translating into measurable savings.
For homeowners, having aragonite instead of calcite in their water systems means less troublesome limescale. While calcium carbonate still precipitates, it does not form hard deposits that require costly cleaning or part replacements. Using appropriate filter cartridges or devices that influence crystallization thus extends the system’s lifespan and reduces maintenance costs.
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