Turquoise

Authors: Audry and Olivia

Mineral Name: Turquoise

Chemical Composition: CuAl6(PO4)4(OH)8·4H2O

Color: Turquoise scales from sky blue to yellowish green. The “greening” or “yellowing” of turquoise is caused by iron. Turquoise is often contained in a host rock that is dark brown or black.

Streak: Bluish white to greenish white

Hardness: Turquoise ranks 5 to 6 on the Mohs scale of hardness. Although Turquoise is fairly hard, it is actually quite brittle, meaning it's easier to break then it is to scratch.(2)

Cleavage/Fracture: Turquoise has no cleavage; instead it has a conchoidal fracture pattern. This is a type of fracture pattern characterized by a curving fracture plain.

Crystal Form: Turquoise can be found in chunks with an undefined shape, in clusters of rounded nodules or globes, in stalactitic points or tiny pointed crystals, in drusy form (thunder egg like), in rosette form (a group of crystals resembling a rose), and also can be found as ore veins.(3)

Luster: Turquoise usually has a dull, waxy appearance but can also appear somewhat vitreous. (2)

Special Features: Turquoise is soft and porous, and is found in a bright variety of blues, greens and, of course, “turquoise”, the blue-green color the mineral is most known for. Turquoise is also known to be embedded in a dark spider web-like matrix.

Varieties: Varieties of turquoise include Agaphite and Ferrian Turquoise. Agaphite is a variety of Iranian turquoise that is more vitreous than regular turquoise. Ferrian Turquoise, also called

Henwoodite or Rashleighite,is a variety of turquoise named for the presence of iron in its composition. Both Agaphite and Ferrian Turquoise are far more rare than traditional turquoise.

Mineral Group: Turquoise is a part of two mineral groups; the turquoise group and the phosphates group. The turquoise group consists of five minerals that all have a similar chemical composition to turquoise, the mineral that names the group.(1) Turquoise is a part of the phosphate group because it contains the phosphate radical of (PO4). A radical, as it relates to minerals, is a compound of elements that acts as one atom to form minerals.(3)

Environment: Turquoise is a secondary mineral that forms from the weathering and dissolution of preexisting minerals. Turquoise is usually formed in arid environments when water evaporates, leaving copper to bond with aluminum and phosphorus, depositing newly formed turquoise on to a host rock in a process called hydrothermal replacement.(3)

Associated Rock types: Because turquoise is a secondary mineral it forms inside of other sedimentary and metamorphic rocks. Copper and aluminum veins will contain turquoise because of their role in turquoise composition. The webbing pattern often found in turquoise is the host rock that the turquoise formed in . The host rocks that are most often associated with turquoise are rhyolite, limestone, quartz-bearing rock and chert. (6) Often copper mining operations will find turquoise and, if there is a large enough quantity of a good quality turquoise, then a second company will come in to mine the turquoise.(1)

Occurrence in North America: The highest concentration of active turquoise mines in the United States are in California, Nevada, Arizona, Utah, and New Mexico.

Economic Uses: Turquoise is considered a desirable stone for use in jewelry and art, such as sculptures and inlays, across many cultures (1). Because turquoise is soft, porous, and delicate in its natural state, it’s incredibly common to find turquoise jewelry that has been processed in some way to make it more marketable or durable. It absorbs dye easily, and is sometimes stabilized or reconstituted by being mixed with polymer or other material that makes it more durable for jewelry-making (1). Pure, natural turquoise is coveted, and is typically found at a much higher price than in its other processed forms. Similar-looking stones are commonly dyed in order to be passed off as turquoise, and these imitation stones have caused distrust in buyers and have had an adverse effect on the market for turquoise.

History of Turquoise: One of the first recordings of turquoise in history dates back to 1519 in Mexico, when Hernan Cortés, the spanish explorer, was gifted the gemstone among other lavish presents by the Aztecs.(5)Throughout history turquoise was believed to have powers that include being able to win the favor of gods (Tibet), make its wearer victorious in fights, protect against harm and make the wearer more likeable. (5) Historically, Persian Turquoise was considered the finest type of turquoise, and therefore is the type of turquoise that appears most often in historical relics. The most notable use of Persian Turquoise is considered to be the crown that Napoleon Bonaparte gifted to his second wife, Empress Marie-Louise, as a wedding present (5). The 1810 crown set in silver and gold with diamonds and 79 turquoise stones was purchased by the Smithsonian Institution in 1971.(5) As it relates to the US, Native Americans have been mining turquoise for over 1,000 years, using it in jewelry and traditional garments and trading it to places far into ancient Mexico.(5)

First Notable Identification: Archeologists have been digging up turquoise trinkets and jewelry dating all the way back to at least 3,000 years ago (4). The name turquoise derives from the french words “turque” or “turquoise”, which mean “Turkish” (2). This is due to turquoise having been brought to Europe through Turkey after it was first found in the Al-Mirsah-Kah Mountains in Iran.(2) Turquoise gems have been prized by many civilizations over the course of millenia, including ancient Egypt, the Native American tribes, Europe, and Asia. Much like today, turquoise was commonly used to make jewelry--usually for rulers or wealthy people--as well as sculptures and carvings.

How We Identified It: We identified turquoise by its shape, color, and texture. Turquoise in its unprocessed form has an irregular shape and a rough and gritty texture. Its most remarkable quality is its naturally bright variety of blue and green hues with brown, black, or grey veins or flakes. Even the smallest pieces of turquoise boast a unique and dynamic combination of colors.

Don’t Confuse It With: The two minerals that most closely resemble turquoise are howlite and magnesite, but only when they are dyed the classic turquoise color, which they often are. Howlite and magnesite are light grey to white minerals that contain dark veins similar to turquoise and because they are porous they readily accept dye. A good way to distinguish dyed howlite and magnesite from turquoise is by taking acetone to the mineral. If an acetone soaked swab removes dye the mineral is not turquoise. Other minerals that are sometimes confused with turquoise are chalcosiderite and variscite. Both of these minerals are usually found in a host rock, like turquoise, and are similar in color but chalcosiderite and variscite are vitreous and more transparent than turquoise.



Bibliography:

  1. King, Hobart M. Geology.com, geology.com/minerals/turquoise.shtml. Accessed 4 Mar. 2020.

  2. Mindat.org, Rock Seeker, www.mindat.org/min-4060.html. Accessed 4 Mar. 2020.

  3. Friedman, Hershel. Minersals.net, edited by Herman Friedman, www.minerals.net/mineral/turquoise.aspx. Accessed 4 Mar. 2020.

  4. GIA, www.gia.edu/turquoise-history-lore. Accessed 4 Mar. 2020

  5. Harriss, Joseph A. , 1 Feb. 2008, web.archive.org/web/20080201025038/www.geocities.com/harriss75007/turquois.htm. Accessed 4 Mar. 2020.

  6. Pueblo Direct, www.pueblodirect.com/pages/learn-about-turquoise. Accessed 4 Mar. 2020.