Sapphire in Depth
Every color except red
Sapphire is corundum, the same mineral as ruby, and by convention any corundum that is not red gets called sapphire. Blue is what people picture, and it comes from iron and titanium sitting next to each other in the structure and passing charge between them. Chromium and vanadium and iron in other combinations produce yellow, green, purple, and the pink-orange padparadscha, which is the most sought after of the fancy colors.
Kashmir sapphires from a deposit worked briefly in the 1880s set the velvety blue standard and almost never appear on the market. Sri Lanka, Madagascar, Australia, and Montana are current sources. At 9 on Mohs with no cleavage, sapphire is one of the most practical gemstones for daily wear, which is a large part of why it became a common engagement stone.
Treatments and synthetics
Sapphire has been synthesized since 1902 by the Verneuil flame fusion process, and synthetic corundum has been sold in enormous quantities ever since. It is chemically identical and usually distinguishable only by curved growth lines and gas bubbles under magnification. Much older jewelry contains synthetic sapphire without anyone intending to deceive.
Heat treatment is routine. Beyond that, lattice diffusion treatments push titanium or beryllium into the stone at high temperature to change or improve color, sometimes only in a surface layer that can be lost if the stone is recut. Diffusion should always be disclosed and it substantially affects value, so ask for a lab report on anything expensive.
Living with it
For daily jewelry, sapphire is close to ideal. It resists scratching, has no cleavage, tolerates water, sunlight, sweat, and household knocks, and takes warm soapy water and a soft brush without complaint. Ultrasonic and steam cleaning are generally safe on untreated and heated stones, but avoid both on fracture-filled or diffusion-treated material.
Star sapphires, cut as cabochons to show asterism from rutile inclusions, are more included and deserve gentler handling. Look at a star stone under a single point light source, because diffuse office lighting will hide the effect completely.
Meaning and pairings
Sapphire is the September birthstone and is linked to Virgo, Libra, Sagittarius, and Taurus depending on the tradition. It is associated with clear judgment, commitment, and holding to a decision, which is a cooler set of themes than ruby's and matches the same mineral in a different key.
By chakra it works at the throat and third eye for blue material, though the fancy colors get reassigned by their color: yellow to the solar plexus, pink to the heart. It pairs with lapis lazuli for a blue arrangement that is affordable to build, with clear quartz for focus, and with ruby as its natural opposite number. Blue sapphire and moonstone together is a common combination for reflective work.