The name “sapphire” can also apply to any corundum that’s not ruby red, another corundum variety.

Blue sapphire is a striking variety of the corundum mineral species, renowned for its deep blue hues that can range from pure blue to greenish or violetish blue. The term "sapphire" generally refers to any corundum that is not red and thus does not qualify as ruby.

In addition to blue sapphires and rubies, the corundum family includes “fancy sapphires,” which come in a dazzling array of colours such as violet, green, yellow, orange, pink, purple, and various intermediate shades. There are also “parti-coloured” sapphires that display a mix of colours, and some sapphires exhibit a unique colour change, shifting from blue in daylight or fluorescent light to purple under incandescent light. Additionally, sapphires can be found in gray, black, or brown.

Fancy sapphires are generally rarer than blue ones, with certain colours, especially in smaller or larger sizes, being particularly scarce. Despite this, they offer a wide range of choices for those seeking something distinctive beyond traditional hues.

Corundum is composed of aluminium and oxygen, and its natural formation typically excludes silicon, which is common in other minerals. As a result, natural corundum in its pure form is colorless. While colorless corundum was once used as a diamond substitute, it has recently gained popularity as an accent stone.

Colour in corundum arises from trace elements. Blue sapphires, for instance, get their colour from small amounts of iron and titanium, with the intensity of the blue increasing with more iron. Chromium imparts the red colour to rubies and the pink colour to pink sapphires.

The 1990s saw significant discoveries of fancy sapphires in East Africa and Madagascar, which complemented traditional sources like Sri Lanka and Madagascar and expanded the availability of yellow, orange, pink, and purple sapphires. This surge in colourful options has inspired contemporary jewellery designers to create vibrant, rainbow-colored suites.

Corundum can also display a phenomenon known as asterism, or the star effect, where a six-ray star pattern appears on the surface of a cabochon-cut stone. This effect, visible in both rubies and sapphires, results from the reflection of white light off tiny, needle-like inclusions within the gem.

Another intriguing variety is the colour-change sapphire, which shifts colour under different lighting conditions, adding an extra dimension to the diverse corundum family.

Both blue and fancy sapphires are sourced from various exotic locations, including Madagascar, Tanzania, Sri Lanka, Myanmar, and Australia.