Sapphire facts for kids

Quick facts for kids Sapphire
The 422.99-carat Logan sapphire
General
Category	Oxide mineral
Formula (repeating unit)	aluminium oxide, Al2O3
Identification
Color	Every color except for red – which is called a ruby – or pinkish-orange (the padparadscha)
Crystal habit	massive and granular
Crystal system	Trigonal Symbol (32/m) Space Group: R3c
Cleavage	none
Fracture	conchoidal, splintery
Mohs scale hardness	9.0
Luster	vitreous
Streak	white
Specific gravity	3.95–4.03
Optical properties	Abbe number 72.2
Refractive index	nω=1.768–1.772 nε=1.760–1.763, Birefringence 0.008
Pleochroism	Strong
Melting point	2030–2050 °C
Fusibility	infusible
Solubility	Insoluble
Other characteristics	coefficient of thermal expansion (5.0–6.6)×10−6/K

Sapphire is a type of the mineral corundum, an aluminium oxide (Al₂O₃). Sapphires are the same as rubies, except that they are not red.

Sapphire can be found in the ground or it can be made in large crystal. Blue sapphires are the most famous kind, but they can be many different colors, like amber and orange.

Sapphires have a long history. Tradition says that the tablets of the Ten Commandments were made of sapphire, so strong a hammer could not break them, and would break instead if it hit them. The ancient Persians believed that the earth sat on a big sapphire and that the big sapphire made the sky blue.

A lot of ancient people thought rubies made people calm down, as well as cure their bruises.

Sapphires have been used by kings and queens for a long time as a symbol of luck, virtue, wisdom, and holiness. Princess Diana and Princess Anne both received sapphire engagement rings and the British Crown Jewels are full of large blue sapphires, the symbol of kind and wise rulers.

Sapphires represent September. It symbolizes telling the truth and doing what you said you would.

Sapphire is actually just corundum and is one of the hardest minerals on the hardness scale. Since sapphire is the second hardest mineral in the hardness scale, it is sometimes used as a polishing tool.

This mineral is found in gem gravel deposits. These deposits are formed from the heat of metamorphic or igneous rock plateaus. The places where sapphire is formed abundantly are Myanmar, Thailand, India and Sri Lanka. The most costly and beautiful sapphires are shipped from Kashmir, India. In other words, sapphire is mostly found in Asia. Recent findings of sapphire have taken place in Australia, Kenya, and Tanzania.

Sapphire was the first mineral to be lab grown in a strategy called "flame fusion". Another strategy, slightly harder to use, "flux growth" was used to lab grow sapphire.

Heating yellow, light yellow, or colorless sapphire from 1500-1900oc can turn into a dark yellow, gold, golden brown, orange, or a reddish brown colored sapphire. There is a specific kind of sapphire called Star sapphires have whitish pieces of rutile or silk as some call it. Star sapphires can be heated to remove the blue color of sapphire and can be heated even more to get the blue color back and remove the white silk.

Mining

Sapphire from Madagascar

Sapphires are mined from alluvial deposits or from primary underground workings. Commercial mining locations for sapphire and ruby include (but are not limited to) the following countries: Afghanistan, Australia, Myanmar/Burma, Cambodia, China, Colombia, India, Kenya, Laos, Madagascar, Malawi, Nepal, Nigeria, Pakistan, Sri Lanka, Tajikistan, Tanzania, Thailand, United States, and Vietnam. Sapphires from different geographic locations may have different appearances or chemical-impurity concentrations, and tend to contain different types of microscopic inclusions. Because of this, sapphires can be divided into three broad categories: classic metamorphic, non-classic metamorphic or magmatic, and classic magmatic.

Sapphires from certain locations, or of certain categories, may be more commercially appealing than others, particularly classic metamorphic sapphires from Kashmir, Burma, or Sri Lanka that have not been subjected to heat-treatment.

The Logan sapphire, the Star of India, The Star of Adam and the Star of Bombay originate from Sri Lankan mines. Madagascar is the world leader in sapphire production (as of 2007) specifically its deposits in and around the town of Ilakaka. Prior to the opening of the Ilakaka mines, Australia was the largest producer of sapphires (such as in 1987). In 1991 a new source of sapphires was discovered in Andranondambo, southern Madagascar. That area has been exploited for its sapphires started in 1993, but it was practically abandoned just a few years later—because of the difficulties in recovering sapphires in their bedrock.

In North America, sapphires have been mined mostly from deposits in Montana: fancies along the Missouri River near Helena, Montana, Dry Cottonwood Creek near Deer Lodge, Montana, and Rock Creek near Philipsburg, Montana. Fine blue Yogo sapphires are found at Yogo Gulch west of Lewistown, Montana. A few gem-grade sapphires and rubies have also been found in the area of Franklin, North Carolina.

The sapphire deposits of Kashmir are well known in the gem industry, although their peak production took place in a relatively short period at the end of the nineteenth and early twentieth centuries. These deposits are located in the Paddar Valley of the Jammu region of Jammu and Kashmir in India. They have a superior vivid blue hue, coupled with a mysterious and almost sleepy quality, described by some gem enthusiasts as ‘blue velvet”. Kashmir-origin contributes meaningfully to the value of a sapphire, and most corundum of Kashmir origin can be readily identified by its characteristic silky appearance and exceptional hue. The unique blue appears lustrous under any kind of light, unlike non-Kashmir sapphires which may appear purplish or grayish in comparison. Sotheby's has been in the forefront overseeing record-breaking sales of Kashmir sapphires worldwide. In October 2014, Sotheby's Hong Kong achieved consecutive per-carat price records for Kashmir sapphires – first with the 12.00 carat Cartier sapphire ring at US$193,975 per carat, then with a 17.16 carat sapphire at US$236,404, and again in June 2015 when the per-carat auction record was set at US$240,205. At present, the world record price-per-carat for sapphire at auction is held by a sapphire from Kashmir in a ring, which sold in October 2015 for approximately US$242,000 per carat (HK$52,280,000 in total, including buyer's premium, or more than US$6.74 million).

Applications

Windows

Cermax xenon arc lamp with synthetic sapphire output window

Wristwatch with synthetic sapphire watch crystal

Synthetic sapphire – sometimes referred to as sapphire glass – is commonly used as a window material, because it is both highly transparent to wavelengths of light between 150 nm (UV) and 5500 nm (IR) (the visible spectrum extends about 380 nm to 750 nm), and extraordinarily scratch-resistant.

The key benefits of sapphire windows are:

• Very wide optical transmission band from UV to near infrared (0.15–5.5 µm)
• Significantly stronger than other optical materials or standard glass windows
• Highly resistant to scratching and abrasion (9 on the Mohs scale of mineral hardness scale, the 3rd hardest natural substance next to moissanite and diamonds)
• Extremely high melting temperature (2030 °C)

Single-crystal sapphire boule grown by the Kyropoulos method. Approximately 200 millimetres (8 in) in diameter, weighing approximately 30 kg (66 lb). (A second boule is visible in the background.)

Some sapphire-glass windows are made from pure sapphire boules that have been grown in a specific crystal orientation, typically along the optical axis, the c axis, for minimum birefringence for the application.

The boules are sliced up into the desired window thickness and finally polished to the desired surface finish. Sapphire optical windows can be polished to a wide range of surface finishes due to its crystal structure and its hardness. The surface finishes of optical windows are normally called out by the scratch-dig specifications in accordance with the globally adopted MIL-O-13830 specification.

The sapphire windows are used in both high-pressure and vacuum chambers for spectroscopy, crystals in various watches, and windows in grocery-store barcode scanners, since the material's exceptional hardness and toughness makes it very resistant to scratching.

In 2014 Apple consumed "one-fourth of the world’s supply of sapphire to cover the iPhone’s camera lens and fingerprint reader".

Several attempts have been made to make sapphire screens for smartphones viable. Apple contracted GT Advanced Technologies, Inc. to manufacture sapphire screens for iPhones, but the venture failed resulting in the bankruptcy of GTAT. The Kyocera Brigadier was the first production smartphone to feature a sapphire screen.

It is used for end windows on some high-powered laser tubes, as its wide-band transparency and thermal conductivity allow it to handle very high power densities in the infrared and UV spectrum without degrading due to heating.

Along with zirconia and aluminum oxynitride, synthetic sapphire is used for shatter-resistant windows in armored vehicles and various military body armor suits, in association with composites.

One type of xenon arc lamp – originally called the "Cermax" and now known generically as the "ceramic-body xenon lamp" – uses sapphire crystal output windows. This product tolerates higher thermal loads and thus higher output powers when compared with conventional Xe lamps with pure silica window.

As substrate for semiconducting circuits

Thin sapphire wafers were the first successful use of an insulating substrate upon which to deposit silicon to make the integrated circuits known as silicon on sapphire or "SOS"; now other substrates can also be used for the class of circuits known more generally as silicon on insulator. Besides its excellent electrical insulating properties, sapphire has high thermal conductivity. CMOS chips on sapphire are especially useful for high-power radio-frequency (RF) applications such as those found in cellular telephones, public-safety band radios, and satellite communication systems. "SOS" also allows for the monolithic integration of both digital and analog circuitry all on one IC chip, and the construction of extremely low power circuits.

In one process, after single crystal sapphire boules are grown, they are core-drilled into cylindrical rods, and wafers are then sliced from these cores.

Wafers of single-crystal sapphire are also used in the semiconductor industry as substrates for the growth of devices based on gallium nitride (GaN). The use of sapphire significantly reduces the cost, because it has about one-seventh the cost of germanium. Gallium nitride on sapphire is commonly used in blue light-emitting diodes (LEDs).

In lasers

Ti-Sapphire laser in operation at CAS, Prague

The first laser was made in 1960 by Theodore Maiman with a rod of synthetic ruby. Titanium-sapphire lasers are popular due to their relatively rare capacity to be tuned to various wavelengths in the red and near-infrared region of the electromagnetic spectrum. They can also be easily mode-locked. In these lasers a synthetically produced sapphire crystal with chromium or titanium impurities is irradiated with intense light from a special lamp, or another laser, to create stimulated emission.

In endoprostheses

Monocrystalline sapphire is fairly biocompatible and the exceptionally low wear of sapphire–metal pairs has led to the introduction (in Ukraine) of sapphire monocrystals for hip joint endoprostheses.

Historical and cultural references

• Etymologically, the English word "sapphire" derives from French saphir, from Latin sapphirus, sappirus from Greek σαπφειρος (sappheiros) from Hebrew סַפִּיר (sapir), a term that probably originally referred to lapis lazuli, as sapphires were only discovered in Roman times. The term is believed to derive from the root סָפַר (sāp̄ar), meaning "to score with a mark," presumably because gemstones can be used to scratch stone surfaces due to their high hardness.
• A traditional Hindu belief holds that the sapphire causes the planet Saturn (Shani) to be favorable to the wearer.
• The Greek term for sapphire quite likely was instead used to refer to lapis lazuli.
• During the Medieval Ages, European lapidaries came to refer to blue corundum crystal by "sapphire", a derivative of the Latin word for blue: "sapphirus".
• The sapphire is the traditional gift for a 45th wedding anniversary.
• A sapphire jubilee occurs after 65 years. In 2017 Queen Elizabeth II marked the sapphire jubilee of her accession to the throne.
• The sapphire is the birthstone of September.
• An Italian superstition holds that sapphires are amulets against eye problems, and melancholy. Mary, Queen of Scots, owned a medicinal sapphire worn as a pendant to rub sore eyes.
• Pope Innocent III decreed that rings of bishops should be made of pure gold, set with an unengraved sapphire, as possessing the virtues and qualities essential to its dignified position as a seal of secrets, for there be many things "that a priest conceals from the senses of the vulgar and less intelligent; which he keeps locked up as it were under seal."

Notable sapphires

Images for kids

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  Main sapphire producing countries

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  An uncut, rough yellow sapphire found at the Spokane Sapphire Mine near Helena, Montana

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  Teardrop-shaped blue sapphire

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  Pink sapphire

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  Faceted padparadscha

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  Star sapphire

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  68 carat star sapphire in round mogul cut - men's ring version - 750 yellow gold - Russian goldsmith - handmade around 1990

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  Crystal structure of sapphire

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  Sapphire ring made circa 1940

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  Yogo sapphire

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  Synthetic sapphire

See also

In Spanish: Zafiro para niños