Gold is a very rare substance making up only ~3 parts per billion of the Earth's outer layer. (Imagine 1 billion Smarties in one place and only 3 of them were made of gold!). Its rarity and its physical properties have made it one of the most prized of Earth's natural resources.
Gold, like iron, copper, lead, tin is a metal. Metals are good conductors of heat and electricity and are almost all solid at room temperature (with the exception of mercury). They are malleable and ductile.
Gold is heavy - it weighs over nineteen times more than water, and is almost twice as heavy as lead. If you had enough Gold to fill a one litre milk carton, it would weigh 19.3 kilograms, the same volume of milk weighs only one kilogram.
Gold is quite soft. It is slightly harder than a fingernail but not as hard as a coin or glass.
Gold, like most metals, can be hammered into thin sheets (malleable) or drawn out into thin wires (ductile). This has made gold sought after for a wide range of applications, like jewellery and in electronics. "Gold leaf", for example, is gold that has been beaten into a sheet less than one tenth of a millimetre thick. It is then used for lettering on honour rolls in schools, or for putting gold onto picture frames and ornaments.