There’s nothing mystical about the everyday marvel of crystals. In fact, you might be surprised to learn how these structures contribute to our transportation, the transmission of information, our enjoyment of food, our health and well-being, and much more.
The newspaper pull-out headline asked a simple question: “Can a crystal change your life?” As a chemist and crystallographer, my answer is a resounding yes. Though not in the way you may be expecting – and also not in the way that the article was suggesting.
Crystals are essential to our modern lives, but we seldom recognise their presence. Some are obvious – the crystals of salt and sugar in our kitchens, for example. But others are less visible. In fact, crystals contribute to our transportation, the transmission of information, our enjoyment of food, our health and wellbeing, and much more.
The continued interest in crystals as healing or spiritually uplifting totems (driven in part by celebrity endorsements) comes with significant human and environmental costs related to exploitative and unsustainable crystal mining practices in developing nations. And the hard evidence for any crystal-induced well-being effect is non-existent. The very limited studies on well-being and crystals have found that, at best, crystals are very pretty placebos.
Which is not to say they can’t have an uplifting effect, just that the effect is a biological one in the mind of the believer and not something inherent to the crystal.
Crystals are undeniably beautiful and alluring objects, and it’s not surprising they have a certain mystique. But what exactly is a crystal?
A crystal is a solid material that has its atoms, or molecules, arranged in a repeating, highly ordered, three-dimensional structure. Crystals are often considered as geometric objects with clear facets (think a well-cut diamond), but the crystal description can be applied more broadly to other structured materials, including crystalline fat molecules in chocolate (more on that later).
Diamonds are a great example of an ordered crystalline material, where carbon atoms are bonded to other carbon atoms in a connected lattice. The rigid arrangement of the atoms in this structure gives rise to the hard properties of diamond, as the structure will resist pressure.
Diamonds are able to be faceted due to the inherent symmetry of the underlying arrangements of atoms, known as the crystal structure. But differences in the arrangements of facets between neighbouring crystals can lead to fracturing, which is highly undesirable for some crystal applications. A notable example is the use of crystals in modern jet planes – not in the instrumentation, or the windows, but deep inside the engines.
The physics of a modern jet engine require materials of incredible strength. The individual blades contained within the turbine are made from advanced nickel and titanium alloys. Casting these components by conventional methods would create solid materials with a number of crystal grains, and the blades would not stand up to the temperature and pressure extremes required, likely cracking or melting while operating at high speed.
The solution to this problem is to control the crystallisation of each blade to make it an individual single crystal – like a quartz crystal, or a diamond – but in a precision-engineered shape. This method is called directional solidification, where the crystal structure is oriented in the chosen direction. An initial corkscrew “seeding”, which starts the crystallisation, propagates through the molten alloy under carefully controlled temperature conditions to form single crystal blades of phenomenal strength. This technology has also been translated to gas-powered electricity generation, with strong and durable blades increasing the efficiency of operation.
The seeding of crystals as used for turbine blades is also crucial for the device you’re currently using to read this article. Inside all of our gizmos and gadgets are a number of microscopically patterned silicon wafers. These crystalline chips are grown as massive cylindrical single crystals from vats of molten silicon by using smaller seed crystals. The seed is spun and slowly lifted out of a vat of molten silicon, with the crystal growing larger as more liquid silicon turns to solid. This single crystal is called a “boule”, and can be the size of an adult. After cooling, the crystals are sliced into thin wafers, and polished and etched to form microprocessors. This silicon wafer method is also used with doped silicon to make conductive wafers for solar panel cells.
The “seeds” in these examples ensure the directional arrangement of atoms. But it turns out that some materials can crystallise into more than one arrangement of their atoms or molecules. You can think of this like assembling a number of bricks together – the building blocks are the same, but they can be arranged in myriad ways. This property of having multiple crystal forms is known as “polymorphism”.
Polymorphs have subtly different chemical properties that are crucial for their function, including solubility and melting point. And it’s these properties that bring us to one of life’s greatest pleasures – chocolate! The fats in chocolate can arrange into at least six polymorphs, with the temperature of their setting from liquid chocolate determining which polymorph you get.
Well-set chocolate has a glossy surface, and a sharp crack when broken, while poorly set chocolate is dull and crumbly with a less pleasant mouthfeel. Chefs and confectioners go to great lengths to obtain the correct chocolate polymorph, using a process known as tempering, where melted chocolate is cooled from specific higher temperatures while stirring and seeding with other tempered chocolate.
The lower the temperature chocolate is set, the more readily it will melt, which is why choc top ice creams are so messy to eat (read my article on ice cream chemistry in Issue 93 of Cosmos Magazine to learn more).
Crystals are also immensely important for the pharmaceutical industry. Most drugs that we take in a pill or capsule are actually crystalline materials that have been ground and pressed. Apart from the use of crystallisation as a chemical purification technique, the shape of the crystals grown from pharmaceuticals is also important, with blocks greatly preferred over longer needle shaped crystals for their ease of use under factory conditions (to give you an idea, imagine pouring a packet of dried fettuccini down a drain pipe, compared to a pack of gnocchi).
Polymorphism also raises its head in pharmaceuticals, but often for less agreeable reasons. The testing and approval of new drugs is limited to a single polymorph. Clever chemists wanting to avoid the patents of their competitors (or to extend their own patent rights) have patented new polymorphs of established drugs in the hope of extending their commercial advantage. The polymorph pharmaceutical is made of the same active ingredient, but may have very different activity in the body due to differences in polymorph solubility. Production and distribution of the “wrong” polymorph could greatly change the function of a drug, as a change in solubility could result in either a clinically unhelpful underdose or a toxic overdose compared to the approved crystal form.
A notable example of pharmaceutical polymorphs gone wrong is the antiretroviral drug ritonavir, which is used to treat HIV/AIDS. The development and approval of ritonavir focused on a polymorph which became known as “Form I”. A more stable polymorph emerged during manufacturing that had significantly poorer solubility, and the greater stability of this “Form II” meant that the factory was soon incapable of manufacturing the approved polymorph.
The situation became more troubling, as a factory in Italy that had been producing Form I found themselves unable to do so anymore following a visit from scientists from the American factory! The suspicions were that the visiting scientists unknowingly brought tiny seed crystals of Form II with them. Fortunately, through some crystal detective work, the chemists were able to remake Form I, and reformulating ritonavir as a gel capsule has allowed it to remain a useful pharmaceutical. A combination of ritonavir and another pharmaceutical (known as Paxlovid) has just passed Phase 3 clinical trials as a treatment for COVID-19.
So next time you take a medication, chew on a bit of chocolate, fly in an aeroplane, or scroll social media on your phone, spare a thought for the crystals inside. They may just change your life.
Nathan Kilah is a Senior Lecturer in Chemistry at the University of Tasmania. He is passionate about sharing the importance of chemistry in our daily lives.