An inert acrylic placeholder for Ununseptium, element 117 also known as Tennessine.  This is cast in crystal clear acrylic.  The cube measures 50mm and is made by Smart-elements.  This is brand new in the box.  I only removed it to take photos.  This would make a great addition to someones element collection to fill the hole in ones periodic table since an actual sample of Ts is impossible to obtain.