Category Archives: Monday Jewellery Components

Aquamarine – March birthstone

342px-Aigue-marine_Pakistan_180308

Vassil, Wikipedia

Aquamarine (Lat. aqua marina, water of the sea) is the March birthstone and a silicate mineral with the chemical formula Be3Al2(SiO3)6. All minerals of the beryl group consist of beryllium aluminium cyclosilicate and aquamarine is its turquoise or blue variety.

If this mineral has a very deep blue colour, you might find it called maxixe. The beryl minerals belong to the cyclosilicates, a sub-group of silicates, and as the name implies there’s a ring structure in the crystal.

The presence of iron ions alters the colour. Fe2+ ions cause a crystal to look pale blue, whereas Fe3+ make it yellow-golden. A combination of both ions produces a dark blue colour, maxixe. Sunlight or heat treatment lighten the mineral. Aquamarine is transparent and 7.5-8 on the Mohs scale of mineral hardness, with 7-10 being able to scratch the surface of glass, and 1-6 being damaged by a scratching knife along their surface. Diamond is the hardest at 10 and talc the softest at 1.

Aquamarines have been used in royal jewellery for hundreds of years and in the English crown there’s a 920-carat gem. Already at the end of 1300, the first pair of lenses was made from aquamarine for spectacles. The etymology of beryl is quite interesting and the German word for eyeglasses, Brille, might not be so illogical after all.

The crystals found in many locations around the world can become large and the heaviest one of gemstone quality found to date weighs 110.5 kg. The largest cut gem can be seen in the National Museum of Natural History, part of Smithsonian Institute.

Jewellery containing aquamarines can be cleaned quickly under running water. The gemstone is brittle so please treat it with care.

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Topaz – November birthstone

Large_Topaz_Gemstones

Michelle Jo, Wikipedia

Last week we discussed minerals and concluded they are divided into two groups, the silicate minerals with silicon and oxygen in different ratios, and the non-silicate minerals. Topaz, one of November’s two birthstones, is a silicate mineral with the chemical formula Al2SiO4(F,OH)2. Its name originates in St. John’s Island in the Red Sea, Τοπάζιος (Τοpáziοs) in ancient Greek. Topaz is a semi-precious gemstone.

Topaz comes in many colours and mystic topaz means that a colourless gem has been treated to give its surface a rainbow effect (see if you can find it in the picture!). It is transparent and an 8 on the Mohs scale of mineral hardness, with 7-10 being able to scratch the surface of glass, and 1-6 being damaged by a scratching knife along their surface. Diamond is the hardest at 10 and talc the softest at 1.

If you want to see huge topaz crystals in real life, there are many natural history museums around the world that have them in their collections. The largest cut gemstone is The American Golden Topaz of almost 22,900 carat or over 4.5 kg, whereas in 1986 a crystal weighing a whopping 5 tonnes (2 x 1.8 metres) was found in Brazil, a significant source of topaz. Smaller crystals have been found in many locations around the world.

It is enough to clean a topaz quickly under running water. Apparently it’s also beneficial to place it in direct sunshine for a short while, to “recharge it”. Regardless of cleaning procedure, remember it can crack when forced through large temperature changes or when it is slammed hard against another object.

Topaz is the birthstone of November in both the U.S. and U.K.

Minerals

Earth structure

Earth, Wikipedia

We decorate ourselves with pieces of our planet. Many “stones” used in jewellery are minerals, so let’s return quickly to some geography (in my school we didn’t learn geology, so geography it is). Earth is a planet and like all planets it has a crust, the outermost layer. We walk on it (the continental crust) and we swim on top of it (the oceanic crust).

Earth-cutaway-schematic-english.svg

Earth from crust to core, Wikipedia

The crust floats on the mantle, which in turn covers the hot core. The lithosphere consists of rock. Rock and mineral isn’t the same thing. A rock doesn’t have a regular chemical structure and it can be formed from minerals or non-minerals. There are three main types of rock:

  • Igneous rocks: are formed with or without crystallization through the cooling and solidification of magma or lava (Lat. ignis = fire). Minerals have a key position in the formation of these rocks.
  • Sedimentary rocks: are formed in the sediment layers at the surface of the planet during deposition of materials. Most of these rocks contain very few different kinds of major minerals, and common ones are quartz and calcite.
  • Metamorphic rocks: are created through metamorphosis of existing rocks, which can happen for instance due to being under high pressure below rock nearer the atmosphere. Metamorphic minerals form only under those conditions and these so-called index minerals include kyanite and some garnet.

An ore is a rock, which contains minerals with a high concentration of a particular element, typically a metal.

A geode is a geological secondary structure, which occurs in certain sedimentary rocks and volcanic rocks (igneous rocks of volcanic origin). Geodes are highly popular in jewellery at the moment thanks to the sparkly silicates and/or carbonates deposited on the surface.

Gems have so-called ornamental value and they are minerals, either semi-precious stones or precious stones, the latter of which are diamond, ruby, sapphire, and emerald.

Minerals are currently defined as “an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes.” In other words, the foundation of classification of minerals is in differences in chemical composition, crystal structure, and physical properties among others.

The majority of minerals are derived from the crust of the Earth and since its two most abundant elements are the metalloid silicon and oxygen, most minerals are silicate minerals with Si and O in different ratios. The rest are in the non-silicate minerals group, the majority of which are very rare. Some common ones are calcite, pyrite, magnetite, and hematite.

Be happy that someone else takes care of mineralogy, as there are over 4900 species. The vocabulary is also rather challenging, so we’ve scratched the surface only (or should I say crust, heh).

Metals – Silver

Jewellery components - Metals - Silver

Solsken Design Sterling beads on sterling hoops

In this first post on jewellery components, you will learn about chemical properties of silver, how it is used in jewellery, and the price of silver.

Chemical properties

The symbol of the chemical element silver is Ag for Argentum, which refers to grey or shining, and its atomic number is 47. Silver is a metal and you find it among the transitional elements in the periodic system. Like all metals, once it reacts to become an ion, its charge changes from neutral to positive. Metals are charged differently though, with either one, two or three lost electrons from the outermost shell. Silver has only one electron in that shell and, hence, its oxidation number is +1 when reacting with other elements to form compounds.

Silver can not only occur in its pure state, but it exists in several alloys. The alloy is a mixture where the primary constituent is a metal. The same way as in liquids, the primary constituent is called a solvent, whereas the secondary constituent is a solute. The primary metal is also called base or matrix. There can be more than two metals in an alloy and the number is denoted binary, ternary, quaternary, and so on, not including any impurities. If a base metal is abundant enough, the whole alloy takes its name.

Another use of the expression base metal is when describing metals in the context of reactivity in moist air. Noble metals are resistant to oxidation and corrosion, whereas base metals are not. Precious metals on the other hand are described as valuable out of a financial aspect and rare on Earth. Reactivity is compared in an electropotential series (galvanic series) and tarnishing of silver has to do with this (more later in an article on how to care for your jewellery).

Jewellery

So, what about silver alloys, why should you care about them? Jewellery is made from silver alloys, not pure silver, which is why I’m pestering you with this much chemistry. You need to be aware as a consumer, so you know what you are spending your hard-earned money on. In jewellery, silver is considered a precious metal, meaning when I buy components, I need to be able to trust the supplier. And I’m doing my best to earn your trust in turn. I’m not taking this lightly, because there’s the occasional fraudulent product in circulation, pretending to be more pure silver than what it truly is.

Confusing is also how the word silver is used. It can describe a colour, which is something I also do when appropriate, because customers think in those terms and search for products using that word. Silver-coloured when describing components, however, usually means that there is silver as a coat on top of another metal or alloy such as brass or it is an entirely different metal that looks like silver only. I avoid this altogether and state instead the exact components through silver-plated or whatever is appropriate. Honesty and transparency is my aim and therefore all my item descriptions will state even smaller component constitutions such as those of head pins and bead caps.

So far, I haven’t talked about “silver” at all, the silver alloys, but here we go! Sterling silver and Britannia silver, the latter of which I have yet to stumble upon in a supplier’s store, are pure enough to be called fine silver. In the US, the percentage of silver in an alloy has to be at least 90% for it to be called fine silver. Sterling silver (925S or .925) contains 92.5% silver and 7.5% copper, whereas Britannia silver contains 95.8% silver. When some of the copper in sterling silver is replaced by germanium, a metalloid (element between metals and non-metals), you get Argentium sterling silver, which is a patented and trademarked modern alloy. Argentium silver has improved chemical properties and is very tarnish resistant.

Silver can be plated in various ways. To give sterling silver a shiny surface, it can be coated with .999 fine silver (99.9%) or for increased tarnish resistance rhodium, another transitional metal that is extremely rare and also a noble metal. Gold-filled silver has a much thicker gold coat compared to gold-plated silver, but even this will wear off eventually. Usually, gold is bonded to base metals, but occasionally silver is treated this way too. This will be covered in greater detail in the article on gold.

Price

The price of silver is currently rising. There was a low lasting for about a decade starting at the beginning of the 1990’s, but from that point on the price has been climbing steadily. The price of fine silver is measured in troy ounce (oz t), a unit of imperial measure. One troy ounce is defined as 31.1034768 g and I say use the historic unit, although I normally prefer the SI units… In 2001, 1 oz t cost 4.37 USD and today one pays 34.15 USD for it. If you see my pricing adjusted, this could be a reason.

If you have questions on this, please post in the comments and I’ll do my best to answer them! I’m passionate about silver, as it is a gorgeous metal with such a rich look.

This was first published in November 2012.