Amazonite is a green to blue variety of microcline feldspar, a cousin to the more familiar moonstone and sunstone.  The name comes from the Amazon River, where a similar looking material was found historically.  Although amazonite does come from Brazil, it has never been found near the river itself.  Research by scientists in the mid 1980's suggests its green to blue color is caused by trace amounts of lead.  However it is safe to handle though because the metal is locked within its crystal structure.