Portal:Gemology and Jewelry/Selected article

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Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminum, with the chemical formula CuAl₆(PO₄)₄(OH)₈·4H₂O. It is rare and valuable in finer grades and has been prized as a gem and ornamental stone for thousands of years owing to its unique hue. In recent times turquoise, like most other opaque gems, has been devalued by the introduction of treatments, imitations, and synthetics onto the market, some difficult to detect even by experts.

The substance has been known by many names, but the word turquoise was derived around 16th century from the French language either from the word for Turkish (Turquois) or dark-blue stone (pierre turquin). This may have arisen from a misconception: turquoise does not occur in Turkey but was traded at Turkish bazaars to Venetian merchants who brought it to Europe. The colour, however, has been employed extensively in the decorative tiles adorning Turkish places of worship and homes for hundreds of years, beginning with the Seljuks, and the association quite possibly has caused the name to take root.

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Ammolite is a rare and valuable opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of the United States and Canada. It is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral that makes up nacreous pearls. It is one of the three biogenic gemstones, the other two being amber and pearl. In 1981, ammolite was given official gemstone status by the World Jewellery Confederation, the same year commercial mining of ammolite began. In 2004 it was designated the official gemstone of the Province of Alberta. Ammolite is also known as aapoak (Kainah for "small, crawling stone"), gem ammonite, calcentine, and korite. The latter is a trade name given to the gemstone by the Alberta-based mining company Korite International, the first and largest commercial producer of ammolite.

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Diamond is the hardest natural material known to man and the third-hardest known material after aggregated diamond nanorods and ultrahard fullerite. Its hardness and high dispersion of light make it useful for industrial applications and jewelry. About 130 million carats are mined annually, with a total value of nearly USD $9 billion. About 100,000 kg are synthesized annually.

The name diamond derives from the ancient Greek adamas (αδάμας; “invincible”). They have been treasured as gemstones since their use as religious icons in ancient India and usage in engraving tools also dates to early human history. Popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns. They are commonly judged by the “four Cs”: carat, clarity, color, and cut.

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The mineraloid opal is amorphous SiO₂·nH₂O; hydrated silicon dioxide, the water content sometimes being as high as 20% but is usually between three and ten percent. Opal ranges from colorless through white, milky blue, gray, red, yellow, green, brown and black. Common opal is truly amorphous, but precious opal does have a structural element. The word opal comes from the Sanskrit upala, the Greek opallios, and the Latin opalus, meaning "precious stone." Opals are also Australia's National gemstone.

Opal is a mineraloid gel which is deposited at relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, and basalt. Opal is one of the mineraloids that can form or replace fossils. The resulting fossils, though not of any extra scientific interest, appeal to collectors.

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A pearl is a hard, rounded object produced by certain animals, primarily mollusks such as pearl oysters. Pearls can be used in jewelry and also crushed in cosmetics or paint formulations. Pearl is valued as a gemstone and is cultivated or harvested for jewelry. The unique luster of pearls depends upon the reflection and refraction of light from the translucent layers and is finer in proportion as the layers become thinner and more numerous. The iridescence that some pearls display is caused by the overlapping of successive layers, which breaks up light falling on the surface. Pearls are usually white, sometimes with a creamy or pinkish tinge, but may be tinted with yellow, green, blue, brown, purple, or black.

Before the beginning of the 20th Century, pearl hunting was the most common way of harvesting pearls. Now, however, almost all pearls used for jewelry are cultured by planting a core or nucleus into pearl oysters. The largest pearl ever found so far, came from the Philippines in 1934. It weighed 14 lb (6.4 kg) when it was discovered by an anonymous Filipino Muslim diver off the island of Palawan.

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An earring is a piece of jewelry that is worn on the ear. They are worn by both genders, although until recently in western cultures, they were more typically worn by women. Earrings are attached to the ear through a piercing in the earlobe or some other external part of the ear. Common locations other than the earlobe for piercings include the rook, tragus, or across the helix.

Earring components can be made out of any number of materials, including metal, plastic, glass, precious stones and beads. Designs can range from small loops or studs to large plates or dangling items. The size is generally limited by the physical capacity of the earlobe to hold the earring without tearing. People who habitually wear heavy earrings may find that over time, the earlobe and piercing stretch. Earrings are worn around the world in most cultures, both currently and historically. In many cultures, it is common to pierce the ears of young girls soon after birth. This has become somewhat controversial because of its involuntary nature. Although not as common as with females, ear piercing among males has also become popular in North America and Europe.

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