This is a piece of facet grade Australian Sapphire from Inverell. This piece is a parti colour meaning it has both the yellow and blue colours showing. This piece is clean and a skilled cutter could make the best use of both colours being present in the stone.
The sapphire is one of the two or three gem-varieties of corundum, with another one being the red or deep pink ruby. Although blue is their most well-known color, sapphires are made up of any color of corundum except for red. Sapphires may also be colorless, and they are also found in shades of gray and black.