These arsenopyrite crystals are from the Panasqueira Mine – Couto Mineiro Panasqueira, Covilha, Castelo Branco District, Portugal. This is a large tungston and tin mine with four stages of minerallization including a sulfide stage containing arsenopyrite. It is a sulfide that contains the elements Fe, As and S. This specimen consists of a translucent to transparent, glassy, quartz crystal that hosts clusters of brassy-silver arsenopyrite crystals. The crystals have multiple and complex terminations. Their luster is submetallic and bright. This piece measures 2 1/2 x 2 1/8 x 1 5/8 inches or 63 x 54 x 41 mm.