The Marble test is used to determine the stability of which component in water?

• A. Calcium carbonate stability
• B. pH stability
• C. Alkalinity
• D. Turbidity

Answer: (A)

The Marble test directly gauges how water interacts with calcium carbonate, showing whether the water will dissolve calcite or promote its precipitation. In practice, a calcite marble is placed in contact with the water, and observations about whether the marble dissolves or develops a coating indicate the water’s calcium carbonate stability. If the marble dissolves, the water is undersaturated with calcium carbonate (water tends to be corrosive to calcite); if a coating forms, the water is saturated or supersaturated and has a tendency to form scale. This is why calcium carbonate stability is the best match for what the test measures. The test is not a direct measure of pH stability, alkalinity, or turbidity, though pH and alkalinity influence calcite stability.