[5] The word turquoise dates to the 17th century and is derived from the Old French turquois meaning "Turkish" because the mineral was first brought to Europe through the Ottoman Empire.

[7] In professional mineralogy, until the mid-19th century, the scientific names kalaite[10]: 571–572  or azure spar were also used, which simultaneously provided a version of the mineral origin of turquoise.

Dissolved oxygen in the water oxidizes the copper sulfides to soluble sulfates, and the acidic, copper-laden solution then reacts with aluminum and potassium minerals in the host rock to precipitate turquoise.

The classical Iranian deposits are found in sandstones and limestones of Tertiary age were intruded by apatite-rich porphyritic trachytes and mafic rock.

[citation needed] In the rainy winter months, miners face a risk from flash flooding; even in the dry season, death from the collapse of the haphazardly exploited sandstone mine walls may occur.

A significant portion of the Nevada material is also noted for its often attractive brown or black limonite veining, producing what is called "spiderweb matrix".

Turquoise prehistoric artifacts (beads) are known since the fifth millennium BCE from sites in the Eastern Rhodopes in Bulgaria – the source for the raw material is possibly related to the nearby Spahievo lead–zinc ore field.

[26] In Spain, turquoise has been found as a minor mineral in the variscite deposits exploited during prehistoric times in Palazuelos de las Cuevas (Zamora) and in Can Tintorer, Gavá (Barcelona).

[28] Other notable localities include: Afghanistan; Australia (Victoria and Queensland); north India; northern Chile (Chuquicamata); Cornwall; Saxony; Silesia; and Turkestan.

A common belief shared by many of these civilizations held that turquoise possessed certain prophylactic qualities; it was thought to change colour with the wearer's health and protect him or her from untoward forces.

They inlaid turquoise, together with gold, quartz, malachite, jet, jade, coral, and shells, into provocative (and presumably ceremonial[clarification needed]) mosaic objects such as masks (some with a human skull as their base), knives, and shields.

The Ancestral Puebloans (Anasazi) of the Chaco Canyon and surrounding region are believed to have prospered greatly from their production and trading of turquoise objects.

The distinctive silver jewellery produced by the Navajo and other Southwestern Native American tribes today is a rather modern development, thought to date from around 1880 as a result of European influences.

The Persian style and use of turquoise was later brought to India following the establishment of the Mughal Empire there, its influence seen in high purity gold jewellery (together with ruby and diamond) and in such buildings as the Taj Mahal.

Cabochons of imported turquoise, along with coral, was (and still is) used extensively in the silver and gold jewellery of Tibet and Mongolia, where a greener hue is said to be preferred.

Most of the pieces made today, with turquoise usually roughly polished into irregular cabochons set simply in silver, are meant for inexpensive export to Western markets and are probably not accurate representations of the original style.

The Ancient Egyptian use of turquoise stretches back as far as the First Dynasty and possibly earlier; however, probably the most well-known pieces incorporating the gem are those recovered from Tutankhamun's tomb, most notably the Pharaoh's iconic burial mask which was liberally inlaid with the stone.

Set in gold, the gem was fashioned into beads, used as inlay, and often carved in a scarab motif, accompanied by carnelian, lapis lazuli, and in later pieces, coloured glass.

Turquoise, associated with the goddess Hathor, was so liked by the Ancient Egyptians that it became (arguably[clarification needed]) the first gemstone to be imitated, the fair structure created by an artificial glazed ceramic product known as faience.

These excavations, including that of Tutankhamun's tomb, created great public interest in the western world, subsequently influencing jewellery, architecture, and art of the time.

In contemporary Western use, turquoise is most often encountered cut en cabochon in silver rings, bracelets, often in the Native American style, or as tumbled or roughly hewn beads in chunky necklaces.

[citation needed] The oldest evidence for this claim was found in Ancient Egypt, where grave furnishings with turquoise inlay were discovered, dating from approximately 3000 BCE.

[citation needed] In the ancient Persian Empire, the sky-blue gemstones were earlier worn round the neck or wrist as protection against unnatural death.

These fakes are detected by gemologists using a number of tests, relying primarily on non-destructive, close examination of surface structure under magnification; a featureless, pale blue background peppered by flecks or spots of whitish material is the typical surface appearance of natural turquoise, while manufactured imitations will appear radically different in both colour (usually a uniform dark blue) and texture (usually granular or sugary).

Some destructive tests may be necessary; for example, the application of diluted hydrochloric acid will cause the carbonates odontolite and magnesite to effervesce and howlite to turn green, while a heated probe may give rise to the pungent smell so indicative of plastic.

Oiled and waxed stones are prone to "sweating" under even gentle heat or if exposed to too much sun, and they may develop a white surface film or bloom over time.

Backing does not diminish the value of high quality turquoise, and indeed the process is expected for most thinly cut American commercial gemstones.

This process consists of pressure impregnation of otherwise unsaleable chalky American material by epoxy and plastics (such as polystyrene) and water glass (sodium silicate) to produce a wetting effect and improve durability.

Perhaps the most extreme of treatments is "reconstitution", wherein fragments of fine turquoise material, too small to be used individually, are powdered and then bonded with resin to form a solid mass.

Care should therefore be taken when wearing such jewels: cosmetics, including sunscreen and hair spray, should be applied before putting on turquoise jewellery, and they should not be worn to a beach or other sun-bathed environment.