Mercury

Mercury is a silvery metal that stays liquid at room temperature, freezing only at about −39 °C. It has been known since ancient times and is mostly obtained by heating the red mineral cinnabar (HgS). Its symbol, Hg, comes from the Latin hydrargyrum, watery silver.

For centuries mercury filled thermometers and barometers. In electronics, it made fluorescent lamps glow, including the thin cold-cathode tubes that lit earlier LCD televisions before the backlight unit switched to LEDs. But mercury vapor and compounds are poisonous and build up in fish and people, so its use is being phased out under the Minamata Convention, a treaty signed in 2013. A backlight made from an LED strip contains no mercury.