Recently, we detailed the science behind why gemstones appear to our eyes in the colours that they do. But what causes the colour; why is it there at all? It’s worth noting that scientifically perfect specimens of many gemstones are colourless. Here, we’re looking at the chemical elements that seep into various jewels and imbue them with a whole rainbow of hues. Let’s start with a little background on chemical elements.
Whenever you see a chemical composition listed on our website or on your authenticity cards (and anywhere else for that matter), what it’s essentially telling you is the ingredients of the gemstone. They are made up of the elements that all things on Earth are created from, including us as living beings. You’ll probably remember the periodic table of elements from your school days, the diagram that categorises all 118 elements (at the time of writing). Having a basic understanding of elements will help you in understanding how some gems are different from others and how many of them receive their fabulous colours.
Everything you can touch is made up of the elements: a gem, flowers, a car, a magazine, a table, and even gasses. Our bodies, for example, are made of mostly oxygen, with a fair amount of carbon added to the mix. Elements are either pure, such as Diamond which is pure carbon (the periodic symbol being C), or, like our bodies, a chemical compound, which is a mixture of two or more elements. There are only 118 elements so far discovered by science, and therefore everything you see on Earth is made from different cocktails of these 118 ingredients.
There are some pure elements that you can’t see, such as the gasses hydrogen and helium, and then others that you can, such as silver, gold, copper, titanium, iron, nickel, palladium and rhodium. But what is the definition of an element? Let’s try and summarise this in as few words as possible. An element is a substance that is made purely from one type of atom. An atom is the absolute smallest possible amount of a chemical element you could have; therefore, an atom of silver is the smallest amount of silver possible. How big is the average atom? About 100,000 times thinner than the width of a piece of human hair.
Atoms vary from one another based on how the centre of the atom (the nucleus) is composed. This centre is composed of protons and neutrons. Protons are positively charged particles, and neutrons are uncharged particles. The number of protons in an atom dictates its atomic number. Hydrogen (symbol H) is the first element in the periodic table because it only has one positively charged proton, helium (He) is second in the periodic table because its nucleus has two positively charged protons. Lithium (Li) has three protons; beryllium (Be) has four, boron (B) five, carbon (C) six, and so on. Around the nucleus are electrons which orbit it. Imagine the nucleus to be our planet, with hundreds of satellites orbiting around it at breakneck speed, and you get a visual idea of how atoms are structured. To make things simple for us, the number of electrons (the satellites) is always equal to the number of protons (positively charged particles).
Let’s compare two different elements. If you could split open a gold (Au) atom, you would find 79 positively charged protons and 118 uncharged neutrons in its centre (nucleus), around which you would see 79 high-speed electrons orbiting its perimeter. Another metal more commonly found on Earth, iron (Fe), has just 26 protons and 30 neutrons, being encircled by 26 electrons.
Let’s briefly explain molecules and compounds. A molecule is two or more atoms that have joined together. They could be two atoms that are the same or two atoms that are different. Compound elements are formed when two or more different types of atoms join together. A gold bar will have lots of gold atoms joined together, lots of molecules, but it is not a compound because all the molecules are gold (Au). Water, however, is created when two atoms of hydrogen link up with a single atom of oxygen (H2O) this is, therefore, a compound. But it’s also a molecule because there is more than one atom.
Let’s bring this back to gemstones before we get too deep! (Although it is a fascinating subject should you wish to continue learning about this.) The jewel with the most straightforward chemical formula is Diamond, which is pure carbon (C). No other gemstone is made from just one element. Quartz varieties such as Amethyst and Citrine also have a relatively simple formula of one silicon atom and two oxygen atoms (SiO2), which is known as silicon dioxide. This is where we get to how gemstones get their colours, because pure Quartz is silicon dioxide with no additional atoms, and is colourless.
Amethyst gets its regal purple colour from iron impurities that percolate into the gemstone as it forms over many thousands of years. Trace elements are rarely written in the formula of a gemstone. If they were, for Amethyst, which has approximately 30 to 40 parts iron per million, you would see Fe4+ added to the end of the formula. Other gemstones such as Garnet have a more complicated formula of X3Y2(SiO4)3 where X and Y are placeholders for the elements that create the many different species of Garnet. Topaz, which is aluminium, silicon, hydrogen, oxygen and fluorine looks like Al2SiO4(F,OH)2 when written down.
However, the hands-down winner in terms of complicated chemical formulas for gemstones is Tourmaline with (Ca,Na,K,▢)(Li,Mg,Fe2+,Mn2+,Zn,Al,Cr3+,V3+,Fe3+,Ti4+,▢)3(Mg,Al,Fe3+,Cr3+,V3+)6([Si,Al,B]6O18)(BO3)3(OH,O)3(OH,F,O)! The symbol ‘▢’, incidentally, means that this part of the formula is vacant of any element in some, but not all, instances. Here are some popular gemstones, and the atomic level imperfections that give them their beautiful colours.
We hope you enjoyed this look at the elements that help give your jewels such vivid colour, and that it has helped you understand just a little more about nature's most beautiful treasures. You can explore our full range of gorgoeus jewellery pieces by clicking the button below.
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