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The chemical symbol, Hg, comes from the Latin word "hydragyrum" which means liquid silver, it being the most common liquid metal at room temperature. As a liquid, the metal is extremely mobile and dense and as a solid, it is ductile and malleable (mercury has a melting point of -39C). It is a readily accessible element as it occurs in concentrated ores, mercury (II) oxide being decomposed by heating alone at around 500C (i.e. with no reducing agent), at which temperature mercury distils out. The element and many of its compounds are extremely toxic and, as mercury has a relatively high vapour pressure at room temperature, mercury surfaces should always be kept covered to reduce vapourisation.