Arsenopyrite (FeAsS) and enargite (CU3ASS4) are the most common As-bearing sulphide minerals in acid mine drainage environments. Orpiment (AS2S3) and realgar (AsS) are also found. In the environment, these minerals are unstable under oxidising conditions, and significant concentrations of As can be released into groundwater upon weathering. Acidophilic bacteria such as Leptospirillum ferrooxidans have been shown to enhance the dissolution of sulphide minerals in these environments, and could therefore accelerate the release of arsenic.