Hey Redmanti
google "Chlorite clay" and "ferromagnesian minerals" for some not so light reading
Sometimes the green clay can be decomposed slate or in some cases like here in Ballarat it can be a concentration of arsenic from previous ore processing. Gold bearing ore quite often goes hand in hand with arsenic and once washed back into the creeks this stuff tends to stick to the bottom and stain the pipe clay. gloves are always a good idea when dealing with this stuff.
google "Chlorite clay" and "ferromagnesian minerals" for some not so light reading
Sometimes the green clay can be decomposed slate or in some cases like here in Ballarat it can be a concentration of arsenic from previous ore processing. Gold bearing ore quite often goes hand in hand with arsenic and once washed back into the creeks this stuff tends to stick to the bottom and stain the pipe clay. gloves are always a good idea when dealing with this stuff.