bismuth crystal specimen decoration mineral earth science minerals collection bismuth crystal samples christmas gift (cabinet) bismuth crystal specimen decoration mineral bismuth is one of the few materials that have a greater density as a liquid than as a solid. <br> only a few other materials such as water, gallium and germanium, exhibit this property. <br> the trigonal crystal structure accounts for the cubic formations. <br> the iridescent rainbows of colors observed are caused by light scattering off thin <br> layers of bismuth oxide formed when the surface of the hot bismuth reacts with the air. <br> great for teaching about crystals, states of matter or even as a gift! <br>