Calcium Calcium Calcium is a chemical element with symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The
Symbol cues, body language, sound, and other contextual clues. Semiotics is linked with both linguistics and psychology. Semioticians thus not only study what a symbol implies, but also how it got its meaning and how it functions to make meaning in society. Symbols allow the human brain continuously to create meaning using sensory input and decode symbols through both denotation and connotation. Swiss psychoanalyst Carl Jung, who studied archetypes, proposed an alternative definition of symbol, distinguishing it from the term "sign". In Jung's view, a sign stands for something known, as a word stands for its referent. He contrasted this with