When does a pink sapphire become a ruby?

red sapphires are rubies & pink sapphires are not rubies

When it comes to colored gemstones, pink sapphires, and rubies dominate the red end of the light spectrum. While they may share a similar colour palette and composition, they are entirely different from each other because of the intensity of the red hue, availability, origin in some instances, and price. It can be very hard to draw a precise boundary between them as there is no international standard to decide unequivocally which is a ruby and which is a pink sapphire. This is important because of the huge price difference between pink sapphires and rubies.

 same composition, same hardness index, same refractive index

Both pink sapphires and rubies belong to the corundum family, which is composed of aluminum oxide making them the second hardest gemstone after diamond. Therefore they are essentially identical. 

It is the presence of trace elements that determines their colour. Rubies are known for their deep red hue, caused by the presence of chromium. On the other hand, pink sapphires get their delicate pink hue from trace amounts of chromium and iron amongst others. Heat treatment of sapphires can increase their saturation markedly and you will see hot pink and deep magneta hues which weren't available not so long ago.

Ruby is typically found in metamorphic rocks, such as marble or gneiss, as well as in igneous rocks, such as basalt. Some of the most famous ruby deposits are found in Myanmar, Thailand, Sri Lanka, Madagascar, and Tanzania. 

Pink sapphire, on the other hand, is often found in alluvial deposits, which are deposits of sediment that have been transported and deposited by water. Pink sapphire can also be found in metamorphic rocks, like ruby, but is more commonly found in secondary deposits. Some of the major sources of pink sapphire are Sri Lanka, Madagascar, Tanzania, and Myanmar.

it's all about the colour 

The primary difference between pink sapphires and rubies lies in their color variation. Rubies are differentiated by their dominant red hue, ranging from deep crimson to vibrant pinkish-red shades. Pink sapphires, on the other hand, exhibit a range of pink hues, from light pastel shades to intense magenta tones.

true rubies are eyewateringly expensive 

Rubies are considered one of the most valuable gemstones, especially those with a vibrant red color and exceptional clarity. The finest rubies command high prices, often surpassing diamonds in value because large ruby gemstones are extremely rare.

Pink sapphires, while still valuable, are generally more affordable than rubies. Their availability in various shades and sizes makes them a popular choice for those seeking a gorgeous deep pink gemstone without the premium price tag.

so how do I tell if I am buying a ruby and not a pink sapphire?

Channeling my inner chemist, the obvious solution would be to place a threshold  on the amount of chromium detected in the gem, below it is deemed a pink sapphire, and above it is a ruby. But in reality, it's not so easy as gemstone cuts, and variations in the chemical zoning within a gemstone may differ significantly. Then you have the added problem with consistent chemical analysis between labs. 

At present, a recognised gemmologist would have access to colour charts or standardised master stones to compare and decide where the gemstone in question sits on the ruby/sapphire spectrum. This eye comparison is the most straightforward comparison which takes into account the reflections and patterns of a cut stone as opposed to the pure chromium content of rock. 

Price could be an indicator, but plenty of 'light rubies' are actually sapphires with the ruby price tag. Location is another clue, Myanmar, Sri Lanka, and Cambodia are the main sources of ruby. 

It's worth noting that the origin of ruby or pink sapphire can affect its value and desirability in the market. The famous blood pigeon rubies from Myanmar have highly sought after for their rich red colour and high quality, while pink sapphires from Sri Lanka are valued for their light and bright colours.

The demand for lush red and top-notch quality rubies will continue to rise exponentially and so will pink sapphires. While it is easy enough to find pink sapphires under $100ct, rubies can go for many 1000 dollars per carat, so the temptation to sell an intensely saturated pink sapphire at a ruby price is intense. 

So in conclusion, if you are buying a pink sapphire, there really isn't any issues, it becomes a price point you are happy with, but do check the previous newsletter on heat treatment and glass filling of sapphires. 

If you are buying a ruby of significant value to you, then get an independent gemmologist certificate and buy from a reputable dealer. Rubies are notorious for being glass-filled along with their blue brothers so it is something to be aware of when you are looking at an exceptionally clear red stone, proporting to be a ruby at an amazing price.

Finally rubies especially Myanmar/burmese rubies including the famous pigeon blood that have been on the embargo list in the past particularly by the US in reaction to the violation of countless human rights by the military regimes. Although they are freely traded now, it may be a consideraton for a buyer who absolutely wants a stone from a no conflict zone,. Many stones are cut and traded ini Thailand where their provenance becomes vague.