sentence: Gray arsenic is the most common.
sentences_before: Arsenic is found in three allotropes.
sentences_after: It is a brittle, somewhat soft metalloid that is a little shiny. It is a semiconductor. Yellow arsenic is unstable and rare. It is the most toxic allotrope. It is a soft and waxy nonmetal, similar to white phosphorus.
concept_name: gray arsenic
headings: Arsenic Properties Physical properties
categories: Semimetals Chemical elements