Calcium is a soft white-gray metal. It is a solid and is opaque. It is an alkaline earth metal. Its melting point is hotter than most other reactive metals. It is a little harder than lead. It has two allotropes. It does not conduct electricity as well as copper, but is much lighter in weight.
It reacts with water to produce hydrogen and calcium hydroxide. It reacts with water very fast when it is powdered. When it is in a chunk, it starts reacting slowly because calcium hydroxide makes a coating that does not dissolve on the calcium. If a little acid is added to calcium hydroxide, it dissolves it, making the calcium react very fast. It burns when powdered to make a reddish flame. This makes calcium oxide. It also makes calcium nitride when heated. It can react with halogens to make calcium halides like calcium chloride with chlorine.
Calcium forms chemical compounds in the +2 oxidation state. Calcium compounds are colorless. Most calcium compounds are not toxic. They are needed in the human body, actually. They are unreactive as far as calcium ions go.

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