The classic semimetallic elements are arsenic, antimony, bismuth, α- tin (gray tin) and graphite, an allotrope of carbon. The first two (As, Sb) are also considered metalloids but the terms semimetal and metalloid are not synonymous. Semimetals, in contrast to metalloids, can also be chemical compounds, such as mercury telluride (HgTe), and tin, bismuth, and graphite are typically not considered metalloids. Transient semimetal states have been reported at extreme conditions. It has been recently shown that some conductive polymers can behave as semimetals.