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 ADA asserts the best scientific evidence supports the safety of dental amalgam. Clinical studies have not established an occasional connection between dental amalgam and adverse health effects in the general population. In 2002, Dr. Maths Berlin of The Dental Material Commission published an overview and assessment of the scientific literature published between November 1997 – 2002 for the Swedish Government on amalgam and its possible environmental and health risks. A final report was submitted to the Swedish Government in 2003 and included his report as an annex to the full report. In the final report from 2003, Berlin states that