Academic Press dict. of sci. and tech., via WWW, Oct. 18, 2001 (calcium: a common alkaline earth element having the symbol Ca; a fairly soft, silver-white metal found in milk, bone, chalk, and limestone and used as an alloying agent and deoxidizer; compounds are used in cooking, as a bleaching agent, and in making plaster)

The Amer. Heritage dict. of the Engl. lang., via WWW, Oct. 18, 2001 (calcium: Symbol Ca. A silvery, moderately hard metallic element that constitutes approximately 3 percent of the earth's crust and is a basic component of most animals and plants. It occurs naturally in limestone, gypsum, and fluorite, and its compounds are used to make plaster, quicklime, Portland cement, and metallurgic and electronic materials; under element: periodic table shows it as one of the alkaline earth metals)

Wikipedia El calcio (del latín calx, calis, cal) es un elemento químico, de símbolo Ca y de número atómico 20. Su masa atómica es 40,078 u. El calcio es un metal blando, grisáceo, y es el quinto más abundante en masa de la corteza terrestre. https://es.wikipedia.org/wiki/Calcio