Sapphire

Sapphire and ruby are gem varieties of the mineral corundum, which is aluminium oxide (Al2O3). On the Mohs scale it has a hardness of 9, making it harder than every natural mineral except diamond.

Corundum is so hard and resistant to weathering that it can also be found in sedimentary deposits and sedimentary rocks, and the mineral is known for a high density that is unusual for a transparent mineral. Sapphires contain traces of iron, titanium and nickel, which give them a range of colours that includes green, yellow, blue, orange, black and pink. Sapphire and ruby crystals can grow to large sizes, and crystals weighing more than a kilogram have been found. According to the Australian Museum, sapphire and ruby have a refractive index between 1.76 and 1.78 and a specific gravity between 3.90 and 4.00.

The most common crystal form of rough sapphire is a barrel-shaped or spindle-shaped hexagonal pyramid, and the shape of the rough crystal influences the shape and size of the finished stone. Pleochroism means that a gem shows different bodycolors when viewed from different crystal directions, and blue sapphires often show greenish blue and violetish blue pleochroism. The star effect in corundum is called asterism, and it is caused by reflections from tiny, needle-like inclusions that are oriented in several specific directions.

The inclusions most commonly encountered in sapphire are rutile silk and particle clouds, and in some stones the silk or clouds take on a distinct appearance that allows the origin to be accurately determined. The hallmark inclusion of Sri Lankan sapphires is long, slender rutile needles, and this silk is often relatively sparse and evenly distributed, with single needles sometimes traversing an entire stone. Many of the most valuable Kashmir sapphires contain tiny inclusions that scatter light and give the stone a velvety appearance without negatively affecting its transparency.

The Star of India has a milky grey-blue appearance caused by the presence of rutile inclusions, and it is these needle-like rutile inclusions, orientated in several specific directions, that result in stars with four, six or 12 rays. A platinum ring features a round cabochon star sapphire as its centerpiece, and this large Sri Lankan stone displays a rare 12-rayed star probably caused by two sets of mineral inclusions oriented at 30° from each other, while the very dark blue gem weighs 70.79 carats.

Corundum that is red is called ruby, so sapphire is the name given to corundum in every other colour. Alongside blue sapphire and ruby, the corundum family includes the so-called fancy sapphires, which come in violet, green, yellow, orange, pink, purple and intermediate hues, as well as parti-coloured sapphires that show combinations of different colours. Preferred sapphires have strong to vivid colour saturation, regardless of which hue they show.

Some sapphires show the phenomenon called colour change, most often shifting from blue in daylight or fluorescent lighting to purple under incandescent light. Corundum can show a phenomenon called asterism, or the star effect, which usually appears as a six-ray star pattern across the curved surface of a cabochon-cut stone; it can be seen in ruby or any colour of sapphire. Star corundum must be cut as a cabochon to display asterism, and a finished stone's attractiveness depends on the star's orientation and on the cabochon's symmetry, proportions, and finish.

Padparadscha is a rare and valuable pinkish-orange sapphire whose name comes from the Sinhalese word for lotus blossom. The definition of padparadscha has always been debated, and GIA indicates on a Colored Stone Identification and Origin Report when a sapphire meets the criteria to be described as padparadscha.

Sapphire occurs in settings whose character is determined by the deep geological history of the terrains that host them. Nearly nine-tenths of Sri Lanka, one of the classic sapphire sources, is underlain by high-grade metamorphic rocks of Precambrian age, and neodymium and rubidium-strontium dating places that basement between 1,000 and 3,000 million years old. Most of the island's gem deposits are sedimentary in nature, though some primary deposits are related to metamorphic and magmatic rock.

The Ratnapura and Balangoda gem deposits lie within the Highland Complex of Sri Lanka, which forms part of an extensive Precambrian granulite belt of the ancient Gondwana continent related to the Pan-African evolution. That belt also comprises the Kerala Khondalite Belt in southern India, Madagascar, Mozambique, and Tanzania, as well as the Lutz-Holm Bay area in Antarctica.

Almost all of Sri Lanka's gem sources are alluvial and contain rich concentrations of gem-bearing gravels known locally as illam. Gem recovery there takes three main forms: pit mining with narrow pits and galleries or small open-cast workings, mechanized mining in open pits using backhoes or bulldozers and sluices, and traditional river mining.

Occurrence can also be sharply limited in quantity. Each year only a limited amount of new Kashmir sapphire material is found, and just a few pieces reach the market. Many in the gem trade believe that the best available Kashmir sapphire material dates back to five productive years in the 1880s.

Zircon inclusions in sapphires from the Ratnapura and Balangoda placer deposits were dated by laser ablation inductively coupled plasma mass spectrometry and yielded U-Pb ages of approximately 549 million years, suggesting that the zircon formed in a high-temperature event at the end of the Precambrian granulite facies metamorphism of the ancient Gondwana continent and that this event coincides with the crystallization of the sapphires.

Uranium-lead geochronology shows that zircons from Sri Lanka's high-grade metamorphic rocks lost significant lead (Pb) at 550 Ma, with new growth of zircon, monazite, rutile, and garnet between 539 and 608 Ma, the dates of the near-peak metamorphism that created the gemstones in that country.

Sapphire recovery in Australia began with gold miners working the Cudgegong and Macquarie rivers in New South Wales in 1851, though commercial mining in the New England area of that state did not begin until 1919, and production in eastern Australia remained limited until mechanised mining was introduced in the late 1950s.

In the United States, the first sapphires were found in the gravels of the Missouri River in Lewis and Clark County, Montana, in 1865, with later discoveries made on Dry Cottonwood Creek and on Rock Creek and in Yogo Gulch.

Mining of Yogo Gulch sapphires began within a year of their discovery in 1895 and continued for 39 years, until rain damaged the mine so badly that it could not economically recover.

• 1851
  First Australian recovery
  Gold miners extract sapphires on the Cudgegong and Macquarie rivers in New South Wales.^{3Sapphire and Ruby — Australian mineral facts · Geoscience Australia (Australian Government) ↗}
• 1865
  First United States find
  Sapphires are found in the gravels of the Missouri River in Lewis and Clark County, Montana.^{13Gemstones · U.S. Geological Survey (USGS), Minerals Information Archives ↗}
• 1895
  Yogo Gulch
  Discovery of Yogo Gulch sapphires; mining begins within a year and continues for 39 years.^{13Gemstones · U.S. Geological Survey (USGS), Minerals Information Archives ↗}
• 1907
  Blue Giant of the Orient
  A 466 ct blue sapphire, the Blue Giant of the Orient, was supposedly mined from the Ratnapura area of Sri Lanka.^{10Sri Lanka: Expedition to the Island of Jewels · GIA — Gems & Gemology, Fall 2014 ↗}
• 1919
  New England commercial mining
  Commercial mining begins in the New England area of New South Wales.^{3Sapphire and Ruby — Australian mineral facts · Geoscience Australia (Australian Government) ↗}
• 1926
  Blue Belle of Asia
  A 400 ct sapphire said to have been found in a paddy field in the Ratnapura district, the Blue Belle of Asia, was described as having the desirable cornflower blue colour.^{10Sri Lanka: Expedition to the Island of Jewels · GIA — Gems & Gemology, Fall 2014 ↗}
• late 1950s
  Mechanised mining
  Mechanised mining is introduced in eastern Australia.^{3Sapphire and Ruby — Australian mineral facts · Geoscience Australia (Australian Government) ↗}
• June 1998
  The Pride of Sri Lanka
  An 850 ct blue sapphire, the Pride of Sri Lanka, was found in Ratnapura.^{10Sri Lanka: Expedition to the Island of Jewels · GIA — Gems & Gemology, Fall 2014 ↗}
• 2012
  A primary deposit at Kataragama
  A primary sapphire deposit was found by accident during road construction near Kataragama in Sri Lanka, and the government auctioned surrounding plots of land for mining.^{10Sri Lanka: Expedition to the Island of Jewels · GIA — Gems & Gemology, Fall 2014 ↗}

The Star of India, at 563.35 carats, was discovered more than 300 years ago in Sri Lanka, but formed about two billion years ago.^{7Famous Gemstones: The Star of India Sapphire · Gem-A, the Gemmological Association of Great Britain ↗} In October 1964 the Star of India was stolen from the American Museum of Natural History along with more than 20 other precious gemstones and diamonds, but within two days the perpetrators were arrested and one of the three men later led police to a bus locker in Miami where the Star of India and some of the other stolen stones were being stored.^{7Famous Gemstones: The Star of India Sapphire · Gem-A, the Gemmological Association of Great Britain ↗}

The Bismarck Sapphire necklace takes its name from its donor, Countess Mona von Bismarck, an American socialite who married German Count Eduard von Bismarck in the late 1930s.^{14Bismarck Sapphire Necklace · Smithsonian National Museum of Natural History — GeoGallery ↗} She gave the necklace to the Smithsonian in 1967 for display in the Gem Gallery at the National Museum of Natural History.^{14Bismarck Sapphire Necklace · Smithsonian National Museum of Natural History — GeoGallery ↗} The 98.57-carat Bismarck Sapphire is mounted in a platinum necklace designed by Cartier that is set with 312 baguette and round brilliant cut diamonds and accented with 8 square-cut sapphires.^{14Bismarck Sapphire Necklace · Smithsonian National Museum of Natural History — GeoGallery ↗}

Marc Antoine Gaudin synthesised the first rubies by fusing alumina with chromium in 1837, and ten years later Jacques-Joseph Ebelmen made artificial sapphires by fusing alumina with boric acid. The Verneuil process was developed in 1902 by the French chemist Auguste Verneuil and produces a boule of synthetic corundum from finely ground alumina that oxygen carries into an oxyhydrogen flame, where the particles fuse and fall as droplets onto the molten upper surface of the boule. Some residual strain left in a half-boule after splitting is not disadvantageous for gem and most industrial uses, and before 1940 all synthetic corundum was made in Switzerland, Germany, and France, while for several years after the process was discovered all of the production was used for gemstones. The Verneuil flame-fusion process has supplied synthetic corundum since 1902 for mechanical bearings, laser components, optics and windows as well as for jewellery. Synthetic corundum is contained in lasers, which are used in barcode scanners, rangefinders, and printers, for cutting tough materials, and for hair and tattoo removal and in surgery.

Sapphire has traditionally symbolized nobility, truth, sincerity and faithfulness. For centuries sapphire has been associated with royalty and romance, an association reinforced in 1981 when Britain's Prince Charles gave a blue sapphire engagement ring to Lady Diana Spencer. During the Middle Ages the clergy wore blue sapphires to symbolize Heaven, and ordinary people believed the gem attracted heavenly blessings.

In folklore, history, art and consumer awareness sapphire has always been associated with the colour blue, and its name comes from the Greek word sappheiros, which probably referred to lapis lazuli. Sapphire is the birthstone for September and the gem associated with the fifth and forty-fifth wedding anniversaries.