Steel-gray, shiny brittle metal in α-form, dark grey in β-form .
In nature, arsenic is found in the Earth's crust, 1.8 ppm, in minor quantities as elemental arsenic and in minerals such as realgar, orpiment, and arsenolite . The isotope found in nature is 75As (100 %, stable) .
In pure solid form, arsenic exist in the following forms:
α-form: rhombohedral crystal at > 280 °C 
β-form: amorphous structure at < 280 °C