Amalgam (chemistry) gold") would not be extractable from ore using hydro-mechanical methods. Large amounts of mercury were used in "placer mining", where deposits composed largely of decomposed granite slurry were separated in long runs of "riffle boxes", with mercury dumped in at the head of the run. The amalgam formed is a heavy solid mass of dull gray color. (The use of mercury in 19th century placer mining in California, now prohibited, has caused extensive pollution problems in riverine and estuarine environments, ongoing to this day.) Sometimes substantial slugs of amalgam are found in downstream river and creek bottoms by amateur wet-suited
Dental amalgam controversy safety and effectiveness of amalgam restorations. In 2012, the Australian Dental Association published a position paper on the safety of dental amalgam. Their position is that "Dental Amalgam has been used as a dental restorative material for more than 150 years. It has proved to be a durable, safe and effective material which has been the subject of extensive research over this time" and that "amalgam should continue to be available as a dental restorative material". Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) is a scientific committee within the European Commission. In a 2008 document of 74