This aquamarine beryl with cassiterite is from the Pingwu Beryl Mine in the Huya Township, Mt Xuebaoding, Pingwu Co., Mianyang Prefecture, Sichuan Province, China. This mine is well known for its production of mineral specimens that also includes aquamarine. Aquamarine is in the beryl family which also includes emerald and helidor. Trace elements in the crystal lattice produce the different colors. Aquamarine is the blue gem variety of beryl and it contains the elements Be,Al,Si,and O. Cassiterite is an oxide mineral containing the elements O and Sn. It is in the rutile group of minerals. This specimen consists of a muscovite matrix that hosts several aquamarine crystals and a twinned cassiterite crystal. The aqua crystals are tabular, transparent, and have a glass luster. The cassiterite crystal is black with a bright luster. This piece measures 1 3/4 x 1 7/16 x 1 1/8 inches or 45 x 37 x 29 mm.