GEMMOLOGY

At First State Auctions, we offer a wide range of quality jewellery, from some of the most precious minerals on the planet.

The Mohs Scale measures the hardness of materials, from 1 (softest) to 10 (hardest). Diamond, being the hardest natural substance, scores a perfect 10 on this scale. For a full description, see our Grading Scales page.

DIAMONDS
Diamonds are formed deep within the Earth’s crust, at extremely high temperatures and under immense pressure. They shoot to the surface in a very rare event through what’s known as a ‘Kimberlite pipe’ (that’s how the Kimberley region in Australia got its name).  The hardest known mineral, diamonds can only be cut with another diamond. Australia and South Africa are the world’s largest source of rough diamonds, while world supply of is dominated by DeBeers and their central selling organisation – helping create even more demand for these already rare stones.

While ‘colourless’ is everyone’s first image of diamond colour, they can in fact occur naturally in a range of translucent hues. White, blue, yellow, orange, red, green, pink, champagne, cognac – even black. Strong hues are typically termed ‘fancy coloured’ diamonds, and ‘round brilliant’ is the most popular cut due to its 58 facets producing the most ‘fire’!

When it comes to size and value, large diamonds are worth disproportionately more than their smaller counterparts. For example, a 1 carat diamond may be $5000, yet a 2 carat worth $15,000. There are also sharp jumps in price once a diamond reaches a new carat weight milestone, such as a round number. The demand for a 1.05carat diamond is considerably more than a 0.95carat diamond due to this ‘perception effect’, despite the relatively small difference in weight overall. Nevertheless, it is this type of behaviour that keeps diamonds at the top of the gemmology food chain.

BERYL GROUP

EMERALDS
Part of the Beryl gem group, Emeralds are very rare. Weighing in at 7.5 on the Mohs Scale, they are primarily sourced from Colombia and Brazil. In particular, Colombian emeralds are prized fro their high quality – experts can identify a Colombian emerald simply by looking at its inclusions. Many jewellery stores will not carry natural emeralds due to their scarcity, and even if they do, they are likely to be man made.

AQUAMARINES
Closely related to Emeralds, but not nearly as famous, Aquamarine is a delicate blue or blue-green colour, hence its seawater name. Being part of the Beryl group gives it a 7.5 measure on the Mohs Scale, and the gemstone has a transparent quality about it. The main sources for Aquamarines are Brazil and Zambia.

CORUNDUM GROUP

RUBIES
Rubies are part of the Corundum gem family (of which Sapphires also belong). Minerals in this group are very hard, with rubies rating 9 on the Mohs Scale. Various parts of Africa supply rubies, however the most famous location is Burma (Myanmar). As with Emeralds, few stores carry rubies and many of those that do stock man made varieties (value is a small fraction of the natural gem). Value increases dramatically with size, and distinctive silk inclusions distinguish natural stones to those that are man made.

SAPPHIRES
Like Rubies, these famous stones measure 9 on the Mohs scale of hardness. While they can occur naturally in many hues, they are typically known for their blue colour – with ‘sapphire’ originating from the Greek for ‘blue stone’. This colour (and indeed, the distinctive red of a ruby) is simply a result of various trace element impurities within the corundum mineral itself. Thailand, Australia and Sri Lanka are main sources of sapphires, with each region’s stones exhibiting their own distinct appearance.

PERIDOTS
Bright yellow-green in colour, Peridot belongs to the forsterite olivine family. In terms of hardness, it measures 6.5 on the Mohs scale and is one of the few gemstones that come in just one colour. The depth of the green itself depends on the amount of iron in the crystal structure, with the most valuable being a dark olive green. Often mistaken for Emerald, the mineral itself is quite common, however gem-quality Peridot is much rarer. Australia, China and Brazil are the main sources.

OPALS
Australia has the market cornered on Opals, with about 97% of the world’s supply produced here. (They are indeed Australia’s national gemstone!) However, when it comes to colour, Opals are significantly less decisive – with a wide range of possibilities including white, milky blue, gray, red, yellow, green, brown, and black. This interplay of colours results from refraction of light through the internal structure of the stone.

TANZANITE
Highly sought after and in extremely short supply, Tanzanite has a very distinctive bright blue/violet/burgundy appearance. Part of the Zoisite group, it was only discovered in 1967, and adding to its scarcity (and name) is the fact that it is only found in one region in Tanzania. In fact the only known deposit lies in an area measuring 6km long and 1km wide. It measures 6.5 on the Mohs Scale.

TSAVORITE
The Tsavo National Park and Tsavo River give Tsavorite its name, despite actually being first noted in nearby Tanzania (coincidentally in the same year that Tanzanite was discovered). A variety of Garnet, Tsavorite is very much green in colour – and can range from spring pale green through to a deep forest green. It measures 7 on the Mohs Scale.

TOURMALINE
Actually a group of several different but closely related minerals, Tourmaline occurs in more shades of colour than any other gem stone, depending on its structure. Iron-rich Tourmaline will typically be blue/black, while high levels of magnesium result in yellow to brown hues. Classified as ‘semi-precious’, Tourmalines come a number of locations including parts of USA, Africa, Brazil, Afghanistan and Sri Lanka. It measures 7 on the Mohs Scale.

PEARLS

SOUTH SEA, TAHITIAN and AKOYA PEARLS
Pearls are cultured by the insertion of a bead under very precise conditions into an oyster. The oyster then reacts to the foreign body by producing layer upon layer of ‘nacre’ – a secretion for shell building – around it. The process can be either natural or farmed, but due to the ‘by chance’ element of natural pearls, they are rarely commercially farmed. Instead, the bead is inserted manually.
Because of their natural finish, pearls are one of the few gemstones that do not require any cutting or polishing. They are classified by shape: button, drop, baroque (irregular) and round.

CULTURED FRESHWATER PEARLS
These differ from other pearls in that they grow in mussels rather than oysters, and in freshwater not the sea. From there however, the process is similar, with a foreign material entering the mussel and being unable to be expelled. The mollusc then coats it with the same ‘nacre’ substance as its oyster friends. Fresh water pearls are of much lesser value then sea water pearls.

PRECIOUS METALS

GOLD
Highly sought after throughout history, gold needs very little introduction. The cornerstone of many jewellery pieces, its carat weight value is key. 100% gold is 24 carats, but due to its inherent softness in this form, it will usually be teamed with other base metals to make it viable for jewellery – see below.
24 carat – fine gold (100% gold).
18 carat yellow gold – 18/24 parts gold (75% fine gold, 25% other alloys)
18 carat white gold – 18/24 parts gold (75% fine gold, 25% alloys such as Palladium, Nickel and Silver to give the white appearance). 18 carat white gold always retains a very faint yellow colour due to the large percentage of fine gold it contains. For this reason it is common practice in the jewellery trade to plate 18 carat white gold with rhodium. With use and over time, this plating will wear off, leaving the faint yellow colour of the 18ct white gold to appear. It is inexpensive to have your jewellery polished and plated again by your jeweller.
9 carat – 9/24 parts gold (37.5% fine gold, 62.5% other alloys)

PLATINUM
As followers of music albums may be familiar with, to ‘go platinum’ is a step up again from gold, and this white metal is indeed extremely rare and even more expensive than white gold. Platinum is usually 90% or 95% pure, with other alloys added to it to increase hardness. In its natural state, it is often mistaken for silver, and its resistance to tarnishing and wear makes it perfect for fine jewellery.