This stunning Vivianite measures 2 1/2 in x 2in approximately. It has a deep green/blue color. It has remains of hydrothermal iron concretion (brown). 

They form in nodules at a region called Cabeça do Cachorro, at São Gabriel da Cachoeira, Amazonas, Brazil.

When exposed to light, Vivianites can loose their clarity and turn opaque.