Diamonds are a girl's best friend

THE CHINGCHOK Hunter

As the leading line from the movie says:

Men grow cold

As girls grow old,

And we all lose our charms in the end.

But square-cut or pear-shaped,

These rocks don't loose their shape.

Diamonds are a girl's best friend.

Diamonds Are A Girl's Best Friend, as sung

by Marilyn Monroe in the 1953 movie,

Gentlemen Prefer Blondes

I can't imagine that there is a human being out there who doesn't appreciate precious gemstones. Minerals, especially in the form of gemstones, are some of nature's most beautiful creations. The scientific study of their chemical and physical properties, and how they form, is known as mineralogy.

One subdivision of mineralogy is the scientific identification, classification, evaluation and appreciation of gemstones, known as gemmology. And in Thailand, there are many gemmologists, because Thailand has many gemstones among its rocks, many traders of precious stones, and many customers willing to buy. Accordingly, Thailand is a gemmologist's dream come true!

How are gemstones formed?

Gemstones are formed over millennia under intense heat and pressure. Geological processes produce certain conditions under which, if the correct minerals are present, gemstones are formed. There are three rock types: Sedimentary, metamorphic and igneous. Of these, gemstones are formed in igneous and metamorphic rocks.

Gemstones are a combination of different elements in a compound that has the correct properties that crystallise and form colours and reflections of beauty. Gemstones are formed deep underground as that is where conditions are right for the crystallisation process.

Igneous crystals are formed when magma, the hot molten layer of rock under the Earth's crust, cools and solidifies in gaps, or fissures, in the Earth's crust deep underground. The magma, which comes out as lava from volcanoes, is a rich soup of minerals that can give rise to untold numbers and varieties of gemstones.

If the magma finds a gap to cool down, crystallisation occurs and gemstones are formed. The stone type, colour and quality of a gem will be determined by what minerals are present while the magma cools. The incredible depths where the gems are formed means that there is tremendous pressure, which also aids in the formation of precious gems. The fact that they are formed so deep underground and are, therefore, subjected to intense heat and pressure, also aids in a gem's formation.

The slow cooling that forms inside the Earth's crust allows large crystals, or gemstones, to be formed. When lava is produced, the mineral-rich, molten rock cools really quickly and forms very small crystals in rocks such as basalt.

Metamorphic rocks are not as common in the gemmology world as igneous rocks are, but the intense heat and pressure can lead to crystallisation and gemstone formation.

Diamonds can be formed through the metamorphic process (basically enormous heat and pressure of igneous or sedimentary rocks), and carbon-based objects will form diamonds under such heat and pressure.

Jade is also another example of a metamorphic gemstone, although the majority of others you can think of are predominantly igneous. Some, though, can be formed through metamorphosis.

Precious and semi-precious

These are ancient terms used to classify gemstones, based on the rarity of the stone. Diamonds, rubies, emeralds and sapphires are the original "precious" stones, while all other gemstones are semi-precious, although a lot has changed in the gemmology world since these ancient terms were invented.

Thailand and neighbouring Burma have huge deposits of sapphires and constantly provide excellent specimens. There are also newly discovered gemstones that have only recently been classified. One of the newest, and in my opinion, the most beautiful, is tanzanite, a blue stone from the hills of Mount Kilimanjaro in Tanzania.

In all reality, if you own a precious or semi-precious gemstone, you are in ownership of a piece of the Earth that has been in formation over millions of years. All stones are precious to me, and they should be to you, too.

Diamonds

Diamonds are in a league of their own in the precious gem world. Diamonds are made exclusively of the element carbon, although other "impurities" can create various colour varieties. Diamonds are the hardest natural substance. They have a refractive index of 2.4 compared to 2.1 for cubic zirconium and 1.5 for glass.

What this basically means is that light refracts (bends) enormously in diamonds due to its density, when compared to glass and cubic zirconium. If the "cut" is right, that is, the number of facets (which are small, flat windows) a diamond has, a high refractive index can bend white light (sunlight) in all directions and disperse the colours of white light, leading to diamonds having its special sparkle, star-like quality, or fire.

Sapphires

Sapphires are a common, yet much-sought-after gemstone in Thailand, as they are mined extensively here, especially in Kanchanaburi province. They are also mined in many other countries throughout Asia, yet interestingly, their mineral composition can determine exactly which region in which country the stones were mined from.

Although most people associate them with the colour blue, sapphires can come in a variety of colours. The colour we see is the reflected visible light range from a band of colours in the EM (electromagnetic) spectrum in the visible light range. That is, if the violet, blue, yellow and green end of the spectrum is absorbed but the red is reflected, then the stone appears red.

This is the case with red sapphires that have the special name ruby. Essentially though, regardless of whether a stone is a ruby or a sapphire, it is made up primarily of the compound aluminium oxide.

Apart from the red-coloured sapphires known as rubies, sapphires can also be pink, purple, deep blue, light blue or even green and colourless. Their colour is determined by the trace elements in the aluminium oxide compound, so if it contains the element chromium, rubies are the result.

If a sapphire contains vanadium, darker blue and purple stones result. Rarer, pink sapphires have high levels of chromium and are beautiful stones, but the classic, light-blue coloured sapphires are the most sought after and generally more expensive stones, and they are of such a colour due to the presence of iron and titanium.

But whether pink, grey, green, red or blue, sapphires are nonetheless amazing and are in the corundum family of stones, which are the hardest known substance next to diamonds.

As long as the mining of gemstones is ethical and regulated, a gemstone's preciousness is in no doubt. They are nature's most wonderful creation and have formed over millennia. So, regardless of whether the gemstones are precious or semi-precious, look after them properly and appreciate them!

Dave Canavan has an MSc in Behavioural Ecology and is the Head of Secondary at Garden International School. Dave is fascinated by science and loves animals, especially the dangerous kind! You may contact Dave at davidc@gardenbangkok.com .