I have compiled a list of sources for the elements that are available to the amateur chemist. Arsenic will be discussed here.
Arsenic is a highly toxic metalloid that comes in several allotropes. The nonmetallic forms of arsenic are least stable, such as yellow arsenic, while the common metallic gray arsenic predominates. Gray arsenic is a dull solid. When heated in air, it burns to the trioxide. Arsenic dissolves in nitric acid to form the oxide as well. Arsenic is found in a wide range of minerals, and is almost always extracted as a byproduct. For example, arsenopyrite is iron arsenide sulfide. When this is roasted, both arsenic and sulfur oxides are produced. Arsenic was a common poison until an extremely sensitive test called the Marsh test was developed for it. This produces the gas arsine (AsH3) from arsenic-containing materials and later deposits the arsenic on a glass tube. Even a tiny trace of arsenic will produce a notable coloration on the glass surface.
In element form: Lead wheel weights for cars contain about 1/4% arsenic.
In compound form: Old treated wood contains Chromated Copper Arsenate as the treatment chemical. Infrared LEDs contain gallium arsenide as the semiconductor. High frequency microwave circuits may use gallium arsenide components. Chicken meat also can contain arsenic in the form of roxarsone.
Here is my sample of arsenic. It is one of innumerable lead wheel weights that are continually leaching into the environment from road abrasion after being loosened from vehicle tires.