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Phenomenal Gems

Updated: Mar 25, 2021

With sapphires, emeralds, rubies and diamonds hogging all the spotlight, there are many fun gems that often get overlooked.

Have you ever heard of “phenomenal” gems? These stones show optical phenomena like stars, cat’s eyes, play-of-colour and colour change, resulting from a special way they transmit and reflect light. Let's take a closer look!

loose Etheopian pear cut opal showing play of colour on a black background


Gems like star sapphires and star rubies show phenomena called “asterism”- a star with four or six rays, caused by needle-like inclusions. To display this phenomena, a gem must be cut into a round or oval cabochon shape (flat bottom and domed top).

loose round cabochon star sapphire showing 6 ray star on a white background

There are also synthetic (man-made) versions of these, so be careful when purchasing them. Synthetic stones can only be identified by a trained gemologist using special equipment.

Asterism can also occur in quartz, spinel and diopside.


Also known as “cat’s eye”, chatoyancy is similar to asterism, but typically only displays bands across the stone that do not cross over in a star.

Chatoyant gemstones include:

  • cat’s eye chrysoberyl

  • tiger’s eye quartz

loose oval cabochon cat's eye chrysoberyl and loose free-form tiger's eye quartz on a grey background

Once again, look out for synthetic versions as well as imitations like cat’s eye glass.


The most famous example of colour-change can be seen in alexandrite.

The national stone of Russia, was first discovered there in 1833, near the Ural Mountains (which happens to be where I am originally from). It is named after Russia’s Tsar Alexander II and possesses a very special characteristic, it changes colour under different light sources. Green in cool daylight and red in warm candle light, it is know as “emerald by day, ruby by night” and I cannot wait to add one to my collection!

elongated cushion cut fine quality loose alexandrite showing strong change of colour from yellowish green to purplish red, side by side colour change comparison

When it comes to alexandrite, its colour and intensity of colour-change will depend on the quality of the stone. Fine, high quality alexandrite like above is very rare and will show the most dramatic colour change.

This striking phenomena also occurs in colour-change sapphires and colour-change garnets.

Colour-change glass and synthetic alexandrite are imitations and can often be mistaken for a natural stone by an untrained eye.


Opal’s internal structure breaks light into sparkling rainbow colours to display phenomena called “play-of-colour”. It does not show all colours of the rainbow, but rather a combination of blue-green and/or pink.

Glass and imitation opals are very common as well as opal doublets and triplets (assembled from a thin slice of opal and plastic).

This stunning, natural opal and diamond ring featured below is available for purchase with a complementary, third party appraisal, for you piece of mind.

Do get in touch if you fancy treating yourself or a loved one!

round white opal, natural diamond halo, vintage inspired white gold ring by Tsarina Gems, on a white and lace background


To find out more about opal and the creation of this ring, visit my previous post:



A broad colour flash that shifts with the gems’s movement is know as labradorescence, as seen below in labradorite. This phenomena is often compared to the iridescent pattern of a butterfly's wing.

Labradorite was first discovered in 1770, off the coast of Labrador in Canada. It is plentiful but relatively unknown. When used, it can often be seen in carvings and some jewellery.

loose free form labradorite showing labradorescence on a white background


Moonstone's internal structure scatters the light and creates a captivating blue sheen know as adularescence. It is often sold as cabochons, beads and carvings. When you move it around and view it under different angles, the misty light seems to roll over the moonstone's surface.

The word adularia comes from Mt. Adular in Switzerland, where the first sources of fine quality moonstone was discovered.

Art Nouveau inspired broach, yellow gold and 9 oval moonstone on a grey background

Moonstone was very popular during the Art Nouveau Era, favoured by the romantics. Although it was overlooked during the Art Deco Era, it regained popularity during the 1960s "flower child" movement and 1990s New Age inspiration.


Do you know which jewellery era is your favourite?

Check out this post to find out!


Although I would not necessarily recommend these gemstones for everyday-wear or engagement rings, they are good to have on your radar if you fancy something very unique and different. Availability might be limited depending on the stone.

For any questions or requests, do get in touch with me via Tsarina Gems Homepage

Visit my Gallery for more inspiration

Check out my Instagram page for jewellery ideas


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