Amethyst

Amethyst is a purple variety of quartz, one of the most abundant and widely recognised minerals in the world. Its distinctive purple colour ranges from delicate lilac and lavender to rich violet and deep reddish-purple. The colour is primarily associated with trace amounts of iron within the quartz crystal. 

How does the colour of Amethyst form? 

• Iron : Essential to the development of Amethyst's characteristic purple colour. 

• Natural Irradiation : Exposure to radiation over geological time alters the iron within the crystal and creates different shades of purple.

• Heat : When Amethyst is exposed to sufficient heat, its colour can change. Depending on the material and conditions, it may become yellow, orange, reddish-brown, or colourless. Heat-treated Amethyst is commonly associated with Citrine.

Another fascinating variety is "Ametrine", a naturally occurring quartz that displays both purple Amethyst and yellow-to-orange Citrine within the same crystal. This distinctive bi-colour appearance develops when different parts of the crystal experience different conditions during formation. Amethyst can occur as transparent crystals suitable for faceting, as well as larger crystal formations and geodes lined with sparkling purple crystals.

Aquamarine

Aquamarine is the blue to blue-green variety of the mineral beryl, belonging to the same mineral family as Emerald and Morganite. Its name comes from the Latin words "aqua marina," meaning "water of the sea," reflecting its tranquil ocean-like colour. Aquamarine ranges from very pale blue to vivid blue and blue-green.

How do the trace elements form the colour of Aquamarine?

• Iron : The principal colouring element responsible for its blue and blue-green hues. Lower concentrations of iron may produce very pale blue Aquamarine, while stronger colour can create a more saturated blue appearance.

Fine Aquamarine is often prized for a clean, transparent appearance combined with a pleasing blue colour. Unlike many coloured gemstones, inclusions are relatively uncommon in high-quality Aquamarine, allowing larger gemstones with excellent clarity to be fashioned. 

Some Aquamarine also displays a subtle greenish undertone, particularly in untreated material. Much of the Aquamarine available today is heat-treated to reduce greenish tones and enhance a purer blue colour. This treatment is widely accepted in the trade and is generally stable under normal conditions.

Garnet

Garnet is a group of closely related silicate minerals rather than a single mineral species. It is best known for its rich red colour, but it can also occurs naturally in a spectrum of colours including orange, yellow, green, purple, pink, brown, black, and even rare colour-changing varieties. 

How do the elements form the colour of Garnet?

• Iron : Forms red, brown, orange, and yellow hues in several Garnet varieties.

• Chromium and Vanadium : Responsible for the highly-sought after vivid green Garnets, "Tsavorite" and "Demantoid".

• Manganese : Often contributes to pink, orange and reddish-orange colours, particularly in "Spessartine" type.

• Calcium : Produces the green "Grossular" and orange "Hessonite" within this distinct mineral species.

Garnets are divided into several major species and varieties, each with its own characteristic colour and composition. "Almandine" is commonly deep red to reddish-purple, "Pyrope" is typically rich red to purplish-red, "Spessartine" ranges from orange to reddish-orange, "Grossular" can occur in green "Tsavourite", orange "Spessartine", yellow and colourless forms, while "Andradite" includes the brilliant green "Demantoid". Garnet can also occur as "Rhodolite," a beautiful pinkish-red to purplish-red variety traditionally associated with the Pyrope-Almandine Garnet series.

One of the most fascinating varieties is Colour-Change Garnet, which can display different colours under different lighting conditions. Another remarkable variety is "Star Garnet," which can display a four-rayed or six-rayed star caused by aligned inclusions within the gemstone. 

Morganite

Morganite is the pink to peach variety of the mineral beryl, the same mineral family that includes Emerald and Aquamarine. Morganite is often valued for its soft pastel appearance and excellent transparency. Its delicate colours range from pale pink and blush to peach, salmon, and soft purplish-pink. 

How do the trace elements form the colour of Morganite?

• Manganese : The principal colouring element responsible for the pink to peach hues of Morganite. The exact balance of colour can vary from a soft pastel pink to a warmer peach or salmon tone. 

Some Morganite may also display subtle purplish or orangey undertones depending on its chemical composition and geological environment. Morganite can be heat-treated to reduce unwanted yellow or orange tones and produce a purer pink colour. The treatment is generally stable under normal conditions.

Rainbow Moonstone

Rainbow Moonstone is a trade name commonly used for a transparent to translucent variety of Labradorite, a member of the feldspar mineral group. 

How does the colourful flash of Rainbow Moonstone form?

• Feldspar Intergrowth : The colourful optical effect is created by microscopic layers and internal structures within the feldspar. As light enters the gemstone, it interacts with these fine layers and is scattered and reflected, producing flashes of colour known as 'labradorescence' or 'schiller'.

The colour of the flash can vary considerably from stone to stone. Blue is particularly common, while fine specimens may display combinations of blue, violet, green, yellow, orange, and other spectral colours. The flash may appear as a concentrated patch, a broad floating glow, or multiple colours radiating through different areas of the gemstone.

One of the most fascinating characteristics of Rainbow Moonstone is its body transparency. When the material is sufficiently transparent or translucent, the colourful flash can appear to originate deep within the gemstone. This can create an almost "lit from within" appearance, with the colours seeming to shift, radiate, and move as the stone or light source changes position.

Peridot

Peridot is the gem-quality variety of the mineral olivine and is one of the few gemstones that naturally occurs in only one main colour family — green. Its colour ranges from yellowish-green and lime green to olive green and deeper green. 

How does the colour of Peridot form?

• Iron : Responsible for the signature green colour of Peridot. The amount and distribution of iron influence whether the gemstone appears more yellowish-green, olive, or a purer green.

The most desirable Peridot is generally characterised by a vivid, saturated green with minimal brown or yellow overtones. Fine examples can display a bright lime-green appearance, while darker material may show a richer olive-green tone. 

Peridot is unusual among gemstones because it forms not in the earth's crust but deep within the Earth's mantle, in magma in the upper mantle (about 20 to 55 miles down the earth's surface),  and is sometimes brought to the surface through volcanic activity. Some Peridot even comes from space inside rare meteorites, making Peridot one of the few gemstones known to have an extraterrestrial occurrence. 

There are a few distinctive characteristics of some Peridots that serve as natural fingerprints of the gemstone. One is the presence of rutile inclusions, which appear as fine, needle-like or hair-like crystals within the stone, forming intersecting patterns or delicate internal structures. Another is lily-pad inclusions, which typically appear as rounded or oval crystals surrounded by circular or radiating fractures, creating an appearance that resembles a lily pad.

Sapphire

Sapphires belong to the corundum mineral family. The iconic blue colour of a sapphire comes from trace amounts of iron and titanium trapped inside a crystal of aluminum oxide, known as corundum. Pure corundum is colourless, while trace elements create its extraordinary spectrum of colours. While best known for blue, it also occurs in fancy colours — "Fancy Sapphire" such as pink, yellow, orange, green, purple, violet, white, grey, deep charcoal/black, and bi-colour "Parti Sapphire." 

How do the trace elements form the colour of Sapphire?

• Titanium and Iron : This combination produces the iconic blue shade. Cornflower sapphires have a perfect balance of these elements, while Ceylon sapphires have lower iron levels due to the soil in Sri Lanka.

• Iron alone : Causes a sapphire to appear greener or yellowish.

• Vanadium : Give rise to purple hues in a sapphire.

• Chromium : Causes a sapphire to turn pink or red (where red corundum is a Ruby).

Another variety is the "Star Sapphire", which is usually cut as a smooth cabochon to display a six-rayed star that moves across its surface as the stone or light turns. This phenomenon, called asterism, is produced when light reflects from fine, aligned inclusions within the stone. Star sapphires occur in blue, black, grey, white, pink, purple, yellow, and green.

Spinel

Spinel is a magnesium aluminium oxide mineral and a gemstone prized for its brilliance and durability. Although traditionally associated with its highly sought after vivid red colour, Spinel can occur naturally in pink, orange, purple, blue, grey, black, and colourless varieties. 

How do the trace elements form the colour of Spinel?

• Chromium : Produces the intense red colour found in fine 'Red Spinel', and can also contribute to vivid pink and reddish-purple hues.

• Iron : Produces blue, grey, brown, and black Spinel. Iron is particularly important in many blue Spinels.

• Cobalt : Responsible for some of the most vivid and highly prized blue Spinels, producing an intense saturated blue colour often referred to as "Cobalt Blue Spinel".

• Manganese : Contributes to pink, orange, and reddish hues in Spinel.

One of the most fascinating varieties is "Colour-Change Spinel", which can shift in colour depending on the lighting environment. Some examples may appear bluish or greyish under daylight and become purplish, pinkish, or reddish under incandescent lighting. 

Tourmaline

Tourmaline is a complex boron-rich mineral group known for its extraordinary range of colours. Unlike many gemstones where one or two elements are mainly responsible for colour, Tourmaline can contain several different trace elements, these elements make Tourmaline one of the widest natural colour spectrums found in gemstones. 

How do the trace elements form the colour of Tourmaline? 

• Iron : Often produces green, blue, brown, and black colours. Iron-rich Tourmalines are associated with 'Schorl', the most abundant black variety. 

• Manganese : Responsible for many pink, red, and orange hues, particularly in 'Elbaite' Tourmaline. 

• Chromium and Vanadium : Produce vivid green colours, sometimes creating exceptionally bright "Chrome Tourmaline".

• Copper : Creates the remarkable electric blue to blue-green colours of "Paraíba Tourmaline", one of the most distinctive and sought-after varieties of Tourmaline. 

Tourmaline is also famous for its ability to display more than one colour within a single crystal. Bi-colour and Tri-colour Tourmalines can show contrasting zones of colour, while "Watermelon Tourmaline" typically displays a green outer zone surrounding a pink or red centre. Another fascinating feature of Tourmaline is its strong pleochroism, where the gemstone can display different colours or intensities when viewed from different directions. 

Zircon

Zircon is a naturally occurring gemstone belonging to the zirconium silicate mineral group. It is one of the oldest minerals found on Earth, with some zircon crystals dating back more than four billion years. Although often associated with its brilliant blue variety, Zircon naturally occurs in a remarkable range of colours including colourless, blue, yellow, orange, brown, red, pink, and green.

How do the trace elements form the colour of Zircon?

• Uranium and Thorium : These elements can become incorporated into the zircon crystal during formation and contribute to changes in its crystal structure over geological time. 

• Iron : Contribute to yellow, orange, brown, and reddish colours in Zircon.

• Rare Earth Elements : Certain rare earth elements can contribute to green and other colours.

Colourless Zircon is highly valued for its exceptional brilliance and strong dispersion, which can produce flashes of spectral colours similar to those seen in Diamond. Blue Zircon is one of the most popular varieties and is commonly produced through heat treatment of naturally brownish or reddish-brown Zircon.

Zircon is sometimes confused with Cubic Zirconia because of their similar names. However, they are completely different materials. Zircon is a natural gemstone and mineral, while Cubic Zirconia is a laboratory-grown diamond simulant made from zirconium dioxide. Another fascinating characteristic of Zircon is its strong birefringence, which can produce a noticeable doubling effect when viewing objects through the gemstone. This optical property, combined with its high brilliance and dispersion, gives well-cut Zircon a distinctive fiery appearance.