The brightness and color intensity can vary from sample to sample.
One very interesting thing about bismuth is that its liquid form is denser than its solid form so as bismuth crystallizes, its solid form floats above the liquid. This effect is only found in 3 other cases (water, gallium, and germanium).
Bismuth was discovered in 1753 by Claude Francois Geoffroy. It is a very unusual and rare heavy metal that is solid at room temperature. Bismuth is rarely found in nature in its elemental form. It is more rare than platinum, ranking number 69 out of the 75 listed rare elements found on Earth’s crust. Bismuth is the most diamagnetic (repels magnets) of all metals. Its thermal conductivity is lower than any metal, except mercury. Bismuth has a high electrical resistance normally and has the highest Hall Effect (increase in electrical resistance when placed in a magnetic field) of any metal. These crystals, while not natural, are nonetheless very interesting and sought after by the mineral hobbyist, collectors and rock hounds. The iridescent coloring ranging through reds, blues, purples, gold and greens is due to a thin layer of bismuth oxide that forms on the surface of the crystal as it cools. This is actually interference coloring, similar to the coloring you see on soap bubbles and on oil slicks, and is based on how thick the oxide grows.