Introduction Sapphires: Origin, Properties and Formation

Sapphires are gemstones from the mineral group corundum (Al2O3). This group also includes rubies, the red variety of corundum. Sapphires, on the other hand, cover all other colours of corundum except red. Sapphires are often perceived as ‘blue sapphires’, but these gemstones offer an impressive range of colours.

History and culture
Since ancient times, the island of Sri Lanka has been an important source of sapphires. Its gemstones were traded to India, the Middle East and as far as Europe. Many of the sapphires found in Byzantine jewellery probably originate from Sri Lanka. Myanmar (Burma) is known for its rubies, but has also supplied outstanding sapphires. Thailand and Cambodia were also important producers, although today they are mainly known for cutting and trading gemstones. The mines of Kashmir, now in India, are famous for their exceptional sapphires, although they are no longer active.

Physical and chemical properties
Sapphires are made of aluminium oxide (Al2O3) and are the second hardest mineral after diamonds, with a Mohs hardness of 9. Pure corundum is colourless, but the presence of trace elements such as iron and titanium gives sapphires their varied colours. The blue colour in a sapphire is created by small traces of iron (Fe2+) and titanium (Ti4+) interacting through a process known as intervalley charge transfer (IVCT).

An important gemmological feature of sapphires is their pleochroism, the property of showing two slightly different colours when viewed from different angles. Many sapphires on the market today are heat-treated to improve their appearance.

Variety of colours
Sapphires offer an impressive range of colours. Sapphires that are not blue are commonly referred to as ‘fancy sapphires’. These include pink, green, padparadscha (pink-orange), orange, violet, purple, black, grey, brown and many other shades in between. The padparadscha sapphire, with its rare pink-orange colour, is particularly sought-after and valuable.

Formation and occurrence
Sapphires form in geological environments that are poor in silicon dioxide but rich in aluminium, as corundum is made up of aluminium and oxygen. Sapphires can occur in a variety of rock types, both metamorphic and igneous. Magmatic rocks are formed when molten lava (magma) rises from the earth's interior to the surface, cools and solidifies. Metamorphic rocks, on the other hand, are formed when existing rocks are transformed by pressure and temperature changes within the earth's crust. However, many high-quality sapphires are not found in the primary parent rock, but in secondary deposits due to erosion and weathering, such as in the gemstone gravel beds of rivers in Sri Lanka.

Today's sapphire mining
In Africa, sapphires were discovered in Tanzania in the 1960s. Madagascar has been one of the world's leading sources of sapphires since the 1990s. In the USA, sapphires were discovered in Montana in the late 19th century. Other important sources are Australia and France.

Research and knowledge of various sapphire deposits enable gemologists to document and characterise sapphires from different deposits. In SSEF, the determination of origin is based on the analysis of microscopic features, trace element concentrations and spectroscopic data of a coloured gemstone. The measured data of a particular stone is then compared with our extensive reference collection and database of coloured gemstones of known origin as well as scientific gemological literature.

Sapphires as an investment
Sapphires are an excellent choice for investors looking for a stable and valuable investment. Their rarity and high demand make them a reliable investment that offers protection and appreciation in times of economic uncertainty and inflation. Sapphires not only offer a fascinating variety of colours, but also a first-class opportunity for asset protection.