Bismuth Crystal Structure – Everything You Need To Know

Bismuth metal is a one-of-a-kind element that is renowned for its applications across a variety of fields, including pharmaceuticals, cosmetics, electronics, and plumbing, to name a few. But although bismuth has many amazing properties and uses, one of the most captivating aspects of this metal is its mesmerizing crystal structure.

Bismuth crystal is recognized for its vibrant colours, as well as its intricate geometric patterns. The shapes bismuth crystals adopt are so interesting and unique that it leaves many wondering how they are formed. If you happen to be one of those curious people, you’re in luck! In this blog, we will be discussing the formation process of bismuth crystals and explore how their seemingly miraculous shapes and structures come to be.

If you’ve ever seen pure bismuth, you’ll know that it doesn’t look like the sparkling multi-coloured pyramid you see in the picture above. Pure bismuth actually has a silvery-white colour and a shape that looks a lot like raw lead. That being said, when pure bismuth is melted down and allowed to cool, it assumes its characteristic staircase-like form and develops its stunning rainbow hues.

Bismuth is a chemical element with the symbol Bi and atomic number 83 on the periodic table, making it a metal with a heavy, but stable nucleus. And although we generally think of metals as being tough and durable, bismuth is in fact quite brittle and malleable.

A trait that is perhaps most responsible for bismuth’s reputation as a malleable element, and by extension use across a variety of applications, is its melting point. Bismuth has a relatively low melting point (271.4°C) compared to other metals. The ease with which bismuth’s melting point can be reached (a stovetop is more than enough) is part of the reason why skilled artists love to experiment with bismuth and create detailed pieces of bismuth jewelry and sculpture.

When pure bismuth is heated to its melting point, it changes states and becomes liquid bismuth. The colourful crystals we love are formed as this molten bismuth cools down and solidifies. During the solidification process, a thin layer, known as the oxide layer, forms on the crystal’s exterior in the same way rust forms on other metals. The only difference is that instead of the earthy, orange tones we associate with rust, the oxide layer on bismuth crystal takes on vibrant iridescent colours.

Before we can discuss the specific crystal structure of bismuth, we must discuss the structure of crystals more generally, starting with unit cells. Unit cells are the basic building blocks that make up the crystal structure of a material. They are like small repeating patterns of atoms that fit together to form a larger three-dimensional structure, much like how blocks fit together to make a tower.

The unit cell determines the overall crystal structure of the specific material. In a crystal, each unit cell is identical and repeats itself throughout the structure. The shape and size of the unit cell, as well as the arrangement of the atoms within it, determine the crystal’s form.

Different materials have different unit cells, and lattice parameters are the measurements of the unit cell, which includes the length of the sides and the angles between them. These parameters define the basic shape and size of the unit cell, which in turn determines the overall structure of the crystal itself.

Bismuth is said to have a rhombohedral unit cell, which means its unit cell is shaped like a rhombus with one angle wider than the other two. Only two of the unit cell’s sides are the same length (90 degrees), while the third side is a bit longer (~120 degrees). This type of crystal structure is not commonly found in other metals or elements, making bismuth’s crystal structure a point of interest for researchers and crystal enthusiasts alike.

Bismuth crystals assume staircase formations because, along with other minerals like gold, galena, and calcite, they are part of a category called hopper crystals. A hopper crystal is a type of crystal formation that has a hollowed-out step-like structure.

Hoppering is an interesting phenomenon that occurs when the electrical attraction of a mineral is higher along its edges than in its face centers. As a result, the crystal edges grow more quickly than the center, as the molecules are pulled towards the exterior of the formation, causing the crystal to take on a hollowed-out, staircase-like shape.

In bismuth’s case, when molten bismuth starts to solidify, its molecular makeup impels it to start building hard edges in order to form a cube. Despite this drive, however, the faces of the crystal are unable to keep up with the rate of growth of the edges, and as a result more edges take shape. The final product of this reaction is the unusually pyramidal structure we associate with the bismuth crystals we find so interesting.

The dry process is a highly efficient method for the extraction of bismuth from its ores, such as bismite and bismuthinite. This process differs from traditional wet processes, as it does not involve the use of liquids or solvents, hence the name ‘dry process.’

The extraction process starts with the heating of bismuth ores to melt the bismuth, which has a relatively low melting point. Once melted, reducing agents, such as carbon or ethanol, are added to the melt to eliminate any oxides or sulfides that may be present in the ore. The choice of reducing agent will depend on the specific characteristics of the ore, and the desired outcome of the extraction process. 

The process is then repeated, with further refining and purification steps, until the pure bismuth metal is obtained. This is a clean and elegant method of extraction. As the oxides and sulfides are eliminated, you are left with high-quality bismuth.

With its captivating crystal structure and unique formation process, bismuth is an element that never fails to impress and interest. At The Bismuth Smith, our deep understanding of bismuth’s elemental properties, from how it melts and liquifies to how it adopts its colourful oxide layer and intricate geometric shapes, lets us create stunning works of bismuth art. 

Our online boutique features a diverse range of bismuth crystals, jewelry and sculptures for you to explore and appreciate. If you’re intrigued by this unique element and its remarkable properties, you should come take a look.

We are certain that you will find something that sparks your curiosity and captures your attention among our assortment of stunning bismuth pieces . So what are you waiting for? Explore what we have available in our online shop and buy bismuth crystals today to experience the enchantment of this fascinating metal for yourself.