This is bismuth — a natural chemical element that chemically resembles arsenic and antimony. But there’s a catch with this crystal.

While bismuth occurs naturally in the Earth’s crust, the striking crystals that capture the imagination of collectors and artists are usually produced through a controlled cooling process in a laboratory. Elemental bismuth may occur naturally, but this type of staircase crystal is usually made in a lab.

Bismuth, a brittle metal with a silvery-white color, is found in the earth’s crust. It’s often as a byproduct of mining other metals such as lead, copper, and tin. Although it’s relatively rare, there aren’t too many applications for them. Bismuth is sometimes used in pharmaceuticals or medicines. For instance, it’s an ingredient in Pepto-Bismol, as well as the 2004 reformulation of Kaopectate — two anti-diarrhea medicines. However, its use is decreasing.

Recently, however, bismuth has become an aesthetic attraction, with beautifully iridescent crystals.

Bismuth crystals

The crystal structure of bismuth is noteworthy. Unlike many metals, which crystallize in a cubic structure, bismuth forms rhombohedral crystals. This means that the crystal lattice is skewed, giving rise to the characteristic stair-step geometry of bismuth crystals. These structural quirks are a direct consequence of the atomic arrangement within the crystal and the conditions under which it forms.

The spiral, stair-stepped structure of bismuth crystals is the result of a higher growth rate around the outside edges than on the inside edges. But this is almost always the result of a synthetic process, not a natural one.

However, synthetic bismuth crystals can take several different geometries.

Artists often create bismuth crystal sculptures by carefully controlling the cooling process to produce specific shapes and sizes. This level of control allows for the creation of intricate designs that highlight the metal’s natural beauty. The result is a fusion of science and art, where the precision of crystal growth techniques meets the creativity of human expression.

But there’s another notable property of these bismuth crystals: iridescence.

Iridescence is a phenomenon where a surface appears to change color when viewed from different angles. This effect occurs due to the interference of light waves reflecting off multiple layers of a material, such as the thin oxide layer on a bismuth crystal. As light waves bounce off these layers, they interfere with one another, amplifying some wavelengths while canceling others. This selective reinforcement and cancellation of light waves produce the shifting rainbow-like colors seen on the surface.

Bismuth exhibits iridescence due to the formation of a thin oxide layer on its surface when it cools and solidifies from its molten state. This oxide layer varies in thickness, causing light waves to interfere with each other as they reflect off the surface.

Unlike many other heavy metals, bismuth is non-toxic and poses minimal risk to the environment. This makes it an attractive alternative in applications where toxicity is a concern, such as in lead-free solder and non-toxic ammunition. This also makes it a pretty safe crystal to have.

For a deeper dive into bismuth and its geological and physical properties, check out our previous feature. If you want to make your own bismuth crystals, here’s how.