Colour Changing Star Garnet
Ever since alexandrite made headlines with the “alexandrite effect”, or simply known as colour change, people have taken note and started discovering more colour changing gemstones. However, most research done upon the “alexandrite effect” were mainly focused on alexandrite, while we know little about other colour changing gemstones. Other colour changing gemstones can range from sapphire, tourmaline, diaspore, and garnet to name a few.
One day at The Gem Museum, as our gem hunter was foraging for gemstones, an extraordinary stone appeared, it was a star garnet AND IT CHANGES COLOUR! Colour change is definitely one of our favorite phenomena and it is always exciting to see one, not to mention a double phenomena stone and it got us all hyped up. We are not sure how rare this type of garnet is, but we do know double-phenomena gemstones are.
In gemology, a star or asterism is only visible when there are one or more sets of dense microscopic needle-like inclusion networks formed within the stone. On top of that, those networks must be aligned to a specific crystallographic orientation in order to reflect the light into a star; Colour change stone changes colour under different illumination, namely daylight and incandescent light, usually due to a reaction of the stone’s trace element.
As seen in the photo, this highly abraded garnet shows signs of how badly it has been taken care of. On the bright side, its colour faintly changes from purple under incandescent light to dark violet under daylight, and a 4-ray star that symbolises an X. Garnet has the most diverse colour-change hue varieties along with alexandrite, although its dramaticness may not be on par with the latter.
Typically garnet does not have a vivid colour change, an attribution defected by its own chemical composition. Based on a research of Madagascan colour change garnets by SSEF, they have concluded that the intensity of its colour change depends on the ratio between manganese and vanadium/chromium. Simply put it as: i) more manganese, less colour change, ii) more vanadium/chromium, more colour change. If the garnet has high content of all three chemical elements, it will show less colour change for manganese overrides the other two.
Although this stone has returned the owner, but it is still an amazing spectacle to see such an awesome gemstone.
Read more here:
Colour Change Garnet – https://www.ssef.ch/wp-content/uploads/2018/03/2001_Krzemnicki_Colour-change_garnets_from_Madagascar_-_Comparison_of_colorimetric_with_chemical_data.pdf
Star Garnet – https://www.ssef.ch/wp-content/uploads/2018/03/2002_Schmetzer_Star_Garnets_and_Star_Garnet_Cat__s-eyes_from_Ambatondrazaka_Madagascar.pdf