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Chemical Elements

The chemical make up of our body is not dissimilar to that of a diamond.


 


For most gemstones in this book we detail the chemical composition on the bottom of each chart. But what do all of those little symbols mean and why do we need to understand anything about them? Having a basic understanding of elements will help you in understanding how some gems are different to others and how many of them receive their fabulous colours.  

So let’s start really basic. Everything you can touch is made up of elements. Your body, a gemstone, flowers, a car, this book, a table: all are made of elements. Even gas and air are made of elements. Our bodies, for example, are made of mostly oxygen, with a fair amount of carbon added to the mix.

Elements, as in the periodic table, are either pure (as in a Diamond which is pure Carbon - the periodic symbol being “C”), or like our bodies a chemical compound; a mixture of two or more elements. There are only 118 elements so far discovered by man and therefore everything you see on earth is made from very similar elements, but just mixed into different cocktails.

There are some pure elements that you can’t see such as hydrogen and helium, and then others that you can such as Silver, Gold, Copper, Titanium, Iron, Nickel, Palladium, and Rhodium.

But what is an element? Well, this book is not about electrochemistry and you really don’t need to be a chemist to get the best out of your gemstones, so 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 nuclei or nucleus) is composed. This centre is composed of protons and neutrons. Protons are simply positively charged particles, and neutrons are uncharged particles. The number of protons in an atom dictates its atomic number. Hydrogen is the first element in the periodic table because it only has one positively charged proton, Helium is second in the periodic table because its nuclei has two positively charged protons, Lithium has three protons, Beryllium has four, Boron five, Carbon six, and so on. Around the outside of the nuclei are electrons which orbit the nuclei. Imagine the nuclei to be our planet, with hundreds of satellites orbiting around it at break neck speed and you kind of understand the principles of how atoms are structured. To make things simple for us, the number of electrons (the satellites) are always equal to the number of protons (positively charged particles).

Let’s compare two different elements. If you could split open a Gold atom, you would find 79 positively charged protons and 118 uncharged neutrons in its centre (nuclei), around which you would find 79 high speed electrons orbiting its perimeter. Whereas another metal more commonly found on Earth Iron, has just 26 protons and 30 neutrons, being orbited by 26 electrons.

You can find out the atomic mass (atomic weight), by adding the number of neutrons and the number of protons together. Helium for example has a relative atomic mass of four (it has two protons and two neutrons) whereas Gold as we can see above has 79 protons and 118 neutrons making its atomic mass 197. Haven’t we learnt a lot in just two pages? We now know how to weigh atoms!

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. Whereas water is made by two atoms of hydrogen linking up with a single atom of oxygen (H20): this is therefore a compound. But it’s also a molecule because there is more than one atom.  

Let’s not go as far as splitting the atom, because that’s way too complex and of no use to us in gemmology. My friend gives an analogy that makes it easy to comprehend elements, atoms, molecules and compounds. You are in an ice cream shop and in the fridge there are 118 different flavours of ice cream, these are your elements to put into your big ice cream cone. One scoop of any of these flavours is your atom. If I want two or more scoops we are going to call my ice cream a molecule. If I want to have one part strawberry and one part chocolate, then it becomes a compound. An element is a basic substance that can’t be simplified (hydrogen, gold, silver etc). An atom is the smallest amount of an element (single scoop of ice cream). A molecule is two or more atoms that are chemically joined together (H2, O2, H2O etc). A compound is a molecule that contains more than one different element (AI2O3 – the chemical compound for Sapphire, etc).

On the following page we have listed elements in order of their Atomic number, along with their symbol and Atomic weight.

The gemstone with the simplest chemical formula is of course Diamond which is pure carbon. No other gemstone is made from just one element. Quartz such as Amethyst and Citrine also has a fairly simple formula SiO2 (Silicon Dioxide). Amethyst then  has a trace of iron impurities which provide the gem with its infamous colour, however small amounts of trace elements are rarely written in the formula of a gemstone. If they were, for Amethyst, which has approximately 30 to 40 parts per million, you would see Fe4+ added to the end of the formula.
 
Other gemstones such as Garnets have a more complicated formula and Topaz which is comprised of aluminium, silicon, hydrogen, oxygen and fluorine looks like Al2SiO4(F,OH)2  when written down. However, the winner in terms of complicated chemical formulae, a gemstone that is a true cocktail of elements is Tourmaline - (Na,Ca)(Mg,Li,Al,Fe2+)3Al6(BO3)3Si6O18(OH)4.

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