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Calcium is dull gray, but it is shiny when scratched. Other physical properties. Calcium is an excellent conductor of electricity. It is very soft and easily scratched. Chemical properties. Calcium reacts rapidly with air to form a coating of gray oxide, and it burns with a red flame.
Calcium hardness (CH) The calcium hardness is a measure of the amount of lime dissolved in the water. Water with a CH of less than. 100 ppm (mg/l) is described as soft water and draws lime out of, for example, the concrete of cast pools and tile. grouting, leading to disintegration.