Gallium arsenide is a semiconductor, used in electronic devices. The sample shown here is a piece with a length of approximately 1 cm. The material itself is dark blue/grey, but it has a very peculiar lustre, not like metal, but more like silicon.

These three pictures show the same sample, but the photograph was made from a different angle. The first picture is from right above, and that reveals the true color of the compound. The other two pictures are from an increasing angle with the vertical line. A brown/red object was placed nearby, and the last two pictures nicely show the reflection of red/brown light from that object.