The Gem Quarter: Understanding Colour – Sunset Magic: Orange & Yellow Gemstones

Brilliant transparent gemstones in warm tropical tones of pale lemon, rich gold, delicate apricot or vivid saffron can be challenging to identify. What could they be?

First in affordability and popularity is the quartz family – from the delicate pastel tones of ‘lemon quartz’ to the vibrant, vivid orange hues of citrine and all shades in-between.

Citrine is commonly confused with a similarly-coloured but more expensive topaz.

Natural citrine is the most valuable form of quartz, and extremely rare. It occurs when amethyst formations are close to natural heat sources in the Earth’s crust.

It ranges in colour from a shade of light gold through to a fiery reddened-yellow and owes its hue to traces of ferric iron.

The majority of citrine on the market, however, is actually heat-treated purple amethyst.

This heat treatment – involving temperatures up to 560 degrees – helps replicate the yellow, gold and amber shades of natural citrine and is clearly recognisable to a trained professional by the subtle stripes that the process leaves on the gemstone.

Heat-treated citrine is readily available, very affordable and extremely durable.

The best specimens of natural citrine come from Brazil, mined in Rio Grande do Sul. Other deposits include Madagascar, the US, Spain and Africa.

Traditionally the darker shades have held more value but recently consumer preference leans towards brighter lemony hues.

Indeed, the name citrine is derived from the French word citrin, meaning lemon-coloured. In this shade, citrine is often confused with orange topaz.

Legend says it acts as an energising stone against issues of willpower, optimism, confidence and self discipline.

There are few references in history to citrine, perhaps because of the stone’s rarity

The first occurrences seem to be the use of citrine by Romans for intaglio and cabochon in the centuries immediately following the birth of Christ.

Citrine saw increased use as a gemstone in jewellery during the Romantic Age (1837-1860).

Today, citrine is widely used in many jewellery styles. The sunny gemstone’s beautiful colours can brighten almost any jewellery style, although it goes particularly well with yellow gold.

An inexpensive gem, citrine is the perfect stone for popular free-form fancy cuts for unique and custommade pieces.

Like all crystal quartzes, citrine has a hardness of 7 on Mohs’ scale and is largely insensitive to scratches. It will also withstand a few knocks, too, since its cleavage properties are non-existent.

The gemstone’s durability makes it a suitable keepsake. Indeed, citrine is the modern birthstone for November and also the stone for the 13th year of marriage.

Like citrine, topaz is the birthstone of November. Yellow topaz is often confused with citrine due to its similar colour

Topaz is allochromatic, meaning it derives colour from impurities and defects in its crystal structure; this explains the vast array of topaz hues.

However, sherry topaz – named after the variety of wine – is perhaps the best-known and most traditional topaz colour, ranging from yellowish brown to orange.

Often, specimens that fall within this colour range are called ‘precious topaz’ to distinguish them from less-expensive citrine.

Topaz has been known as a gemstone for at least 2,000 years and is believed to take its name from the island the Ancient Greeks knew as Topazios – modern day Zabargad.

Scholars also trace its name back to the Sanskrit word tapaz, meaning “fire”.

Brazil is the principal source of gem-quality topaz, with the region Minas Gerais producing large yellow to orange crystals.

Sapphire and garnet

Next comes sapphire, from the corundum family. Like topaz, it is allochromatic.

On the yellow to orange spectrum, colours range from stronglysaturated golden yellows typical in Australia to soft pastel tones seen in Ceylon sapphires.

Other treatments must be disclosed if they significantly alter a gemstone’s appearance and value.

Beryllium surface or sub-surface lattice diffusion has been used since the early 2000s. This treatment transforms lowquality off-colour corundum into beautiful, vibrant yellow or orange using heat treatment in combination with beryllium.

Meanwhile, some of the most vibrant yellow and orange gemstones are from the beloved garnet family.

In its finest quality, spessartite garnet is Fanta-orange, malaya garnet is orange to reddish-orange and hessonite garnet ranges from orange to brownish-yellow to brownish-red.

Spessartite – also known as spessartine – is named for the German region of Spessart, Bavaria, where the mineral was first discovered.

Today, most spessartite garnet originates from Africa, with deposits of high-quality material found Namibia and Nigeria in the 1990s.

In recent times, spessartite deposits are active in Mozambique and Madagascar, though supply is relatively limited.

Spessartite is a manganese aluminum silicate; the element manganese gives it its distinctive orange colour. A mixture of spessartite and iron-rich almandine garnet produces a reddish-orange effect.

Yellow and orange zircon

Zircon is the oldest mineral on earth and Australia boasts the oldest deposits dating back more than 4.4 billion years.

The most famous source of Australian zircon is the Mud Tank Zircon Field, found in an area known as the Harts Range, which is situated 1,220 km south to southeast of Darwin in the Northern Territory of Australia.

This field, first explored in the 1940s, is well-known amongst fossickers for producing top-quality zircon and includes two areas called Zircon Hill and Specimen Hill.

The zircons found here display beautiful earthy tones of cinnamon, sherry, cognac, pinks, plums, oranges, yellow and even parti-coloured and colourless.

Gemstones may occur as small, doubly-terminated crystals or chips, and larger specimens may show well-developed crystal faces. Waterworn zircon crystals occur in the low-lying areas between the two hills.

Zircon is found intermixed with sapphire in deposits associated with tertiary volcanic deposits from Tasmania to Northern Queensland.

This is particularly true on the gemfields of Northern NSW and Central Queensland where they range in colour from colourless through to champagne and orange-red.

Sometimes Australian zircons are heated to lighten them or make them colourless. Most zircon deposits originate from Maynamr (Burma) Burma but other world sources include Sri Lanka, Cambodia, Brazil, Africa, Madagascar, Thailand and Vietnam.

Zircon is prized for its diamond-like lustre, intense fire, brilliance and strong double refraction and it’s these qualities that separate it from its many imitators. Golden brown zircon can appear similar to topaz or citrine.

Zircon sometimes contains traces of uranium, irradiating itself and changing its properties. For this reason, zircon is classified into three types – high, intermediate and low.

Above: Southsea Golden Pearl Strand		Above: Jewellery Theatre

Amber and pearl

As natural gemstones – that is, formed through organic processes – amber and golden South Sea pearls reflect the warm, rich hues found in nature.

Golden South Sea pearls are among the largest and most valuable pearls, grown in the gold-lipped variety of Pinctada maxima oysters over a period of two to four years – far longer than freshwater or Akoya pearl varieties.

Unlike white South Sea pearls, which are primarily farmed in Australia, golden South Sea pearls are predominantly grown in the Philippines and Indonesia, with a minority sourced from Australia and occasionally Myanmar (Burma).

Their natural colour requires no enhancement and is the primary determinant of their value; the richer the golden tone, the more highly prized the pearl.

The deepest golden tone is often referred to as ’24 carat’.

Amber, meanwhile, is one of the more well-known organic gems is fossilised tree resin prized for its rich golden hues.

When plant or animal fragments are suspended within the material, they can offer a fascinating peek into our planet’s primordial past.

It ranges in colour, but the best-known specimens are yellow to yellow-brown.

Chemically, amber is a hydrocarbon – a compound of carbon, oxygen and hydrogen – although the chemical constituents vary between sources worldwide.Unearthed predominantly in the Baltic Sea region of Europe, it is also found in the Dominican Republic, Myanmar (Burma), Mexico and some other European localities.

Not all tree resin is destined to become amber. Much like all fossils, there are specific environmental conditions of heat, pressure and biology that are required for the fossilisation to take place.

The two-part process of transformation from tree resin to amber is called ‘amberisation’.

Over the course of 2–10 million years, the resin begins to harden through a process of molecular polymerisation. Here, the resin must be in an anaerobic (oxygen-free) condition under layers of overlying sediment, where pressure and heat can transform the soft resin into harder and more stable ‘copal’ resin.

From here, sustained heat and pressure can further evaporate terpenes (organic compounds within the resin) to form a hard, solid natural plastic – amber.

Evidence suggests that Baltic and Dominican amber were created in a very specific anaerobic environment – extended immersion under seawater.

While amber may be transparent through to opaque, transparent material is typically the most sought after. The darker, reddish material is more valuable, but inclusions play a huge part in the final value.

Carnelian

Carnelian is a translucent stone available in varying shades that range from flesh pink to burnt orange, red and brown.

It was argued that carnelian’s colour was reminiscent of bloodied human flesh and this explains the derivation of its name: carne being Latin for flesh or meat.

Although the gemstone is comprised primarily of silicon dioxide, it owes its warm tones to the iron oxide impurities it contains.

Deposits of carnelian are found close to the Earth’s surface where conditions are cooler and less pressurised.

Carnelian is a member of the chalcedony family. As microcrystalline forms of quartz, chalcedony gems are among the most abundant on Earth. Consequently, carnelian can be found in numerous countries all over the world.

Uruguay and Japan are among the most popular locations, however the main source of carnelian is Campo de Maia in South America. Many of the specimens derived from here are colour treated with ferrous nitrate to enhance their hue.

Of all the places carnelian is found, India is regarded by the jewellery industry as the place where the best-quality examples are found.

Numerous pieces of jewellery containing carnelian were uncovered in ancient Egyptian tombs. So strong was the Egyptian peoples’ faith in carnelian that, along with turquoise and lapis lazuli, it was the most used stone in ancient Egyptian jewellery.

In the Middle East, many feared the superstitious power of the ‘evil eye’, an amulet comprised of various gems, including turquoise.

Carnelian was carved into pendants and inscribed with prayers that were believed to ward off evil glances.

Modern-day uses see carnelian cut as cabochons and used in all types of jewellery, particularly beads and cameo brooches.

Fire opal

Opal is famous for the incredible array of colours displayed, from vibrant reds – the most prized – to velvety purples and everything in between.

With such incredible opal specimens here in our backyard, international varieties are often lesser known and less available.

Fire opal is the transparent to translucent variety of opal with a yellow, orange, or even ruby red body-colour, also known as ‘Mexican opal’ – derived from the hue and the most well-known locality of this material.

Fire opal rarely displays play-of-colour, yet it attracts collectors based on the body-colour alone – a primary distinction from the better-known types of opal.

Opals with play-of-colour are termed precious opal, whereas those without are called common opal. Although fire opal may be either, the presence of play-of-colour commands a higher price.

The regions of Querétaro and Jalisco in Mexico are major producers of fire opal, though other regions include Michoacán, as well as Bemia in Madagascar, Kazakhstan, Turkey, Ethiopia, Java in Indonesia, and the US state of Oregon.

The opal localities of Mexico were discovered accidentally by labourers around 1835.

Organised mining efforts commenced circa 1870, although it is believed these deposits may have been known to the Mayan and Aztec people who used fire opal in art and ritualistic ceremonies, significantly extending the history of these gemstones.

The vibrant hues are owed to the presence of particularly minute inclusions, coloured by iron.

Given that play-of-colour is less prevalent, and these fire opals are admired for their body-colour, they are often faceted rather than just fashioned into the cabochon or freeform shapes commonly seen in other types of opal.

	Officially the worlds oldest gem, pearls have been surrounded in history, legend and mysticism since before written history, with discoveries such as pearl jewellery found in a royal sarcophagus dating back to 420BCE. Pearls were also often presented as gifts to Chinese royalty as early as 2300BCE, while in ancient Rome they were considered to be a status symbol and laws were passed allowing pearls to be worn only by the ruling classes. The only way of sourcing pearls was by collecting wild oysters. It could take up to a tonne of wild oysters to find just three or four quality pearls. The increasing demand for natural pearls by the 19th Century meant oyster supplies began to decline. In the late 1800s, the concept of culturing pearls was developed, with Kokichi Mikimoto becoming perhaps the most famous for commercialising and marketing this industry. Pearls can be cultured in various species of oyster, in both fresh and saltwater, producing different finished pearls with different attributes – and thus value. Saltwater pearls take up to four years to produce a pearl, with each oyster generally producing just one pearl for each cycle. They are highly sensitive to their environment and subtle changes in their surroundings can directly affect the oyster’s health. Therefore, saltwater pearl farms generally are located in pristine environmental conditions. Golden South Sea pearls are cultured from the gold-lipped Pinctada maxima along the Philippine, Indonesian, and Australian coastlines and are valued for their size and their unique lustre, Source: Atlas Pearls

Read eMag