Identifying Calcium Minerals

Flame Test. When calcium occurs in a mineral in such a state that it can be volatilized by heat, it will yield a characteristic orange flame color. Frequently the mineral has to be moistened by hydrochloric acid before heating. The flame should not be confused with the crimson and more persistent flame of strontium or lithium.

Alkaline Reaction. Calcium is an alkali-earth metal. When a mineral contains calcium in a combination with a volatile acid, it will give, after ignition a residue which will react alkaline on a piece of moistened turmeric paper.

Precipitation as Calcium Oxalate or Carbonate. Calcium is readily and completely precipitated from alkaline solutions as calcium oxalate, CaC₂C₄, or calcium carbonate, CaCO₃, by the addition of ammonium oxalate, (NH₄)₂C₂O₄, or ammonium carbonate, (NH₄)₂CO₃. Both precipitates are white and finely divided.

Precipitation as Calcium Sulfate. Calcium I s precipitated from a concentrated hydrochloric acid solution as calcium sulfate on the addition of a little dilute sulfuric acid. The precipitate is quite readily soluble in wart and therefore will not from in a dilute solution (distinction from barium and strontium).