Tourmaline
Hardness 7-7.5 specific gravity 3.0-3.1
Refractive index 1.62-1.65 birefringence 0.014-21
Wear: good durability
Tourmaline (tourmaline), also known as tourmaline, is a borosilicate with very complex composition. Due to its complex composition and rich color types, there may be several different color areas on the same crystal.
The name "tourmaline" comes from its special physical properties - thermoelectricity and piezoelectricity. When it is heated and pressurized, the two ends of the crystal will be charged, which can absorb dust and small pieces.
Tourmaline is a birthstone of October.
Human understanding of tourmaline
Tourmaline was used in Greece and Rome in 300 BC, and pink tourmaline stones were also found in Nordic tombs around 1000 ad.
In the 17th century, the Dutch East India Company brought Sri Lanka's colored tourmaline to Europe to meet people's pursuit of colored gemstones, but at that time, they did not really know such gemstones.
In 1703, tourmaline was mixed with zircon stone, also from Sri Lanka. The stone cutter found that the stone absorbed dust as soon as it was exposed to the sun. So they asked the Indian who brought the raw stone the name of the ore, and the Indian didn't know the stone, so they answered "turmali", which means "mixed gems" in Sri Lanka. Now the English name of tourmaline comes from this.
Production and origin of tourmaline
Tourmaline is mainly produced in pegmatite and other granites, and gem tourmaline is mainly produced in Brazil, Afghanistan, Madagascar, Myanmar, Mozambique, the former Soviet Union, Xinjiang, China, etc.
Brazil is the main producer of gem grade tourmaline, whose mining history can be traced back to about 1500 years.
The color and variety of tourmaline
Tourmalines are very rich in color, which can be of various colors. Tourmalines of different colors also have their own names in English, such as "rubellite", "verdelite", "indigolite", colorless "achroite", pink and green "watermelons". In addition, black tourmalines are called "Schorl" is rarely used to make gems.
In 1989, a new type of tourmaline, Paraiba tourmaline, was found in the state of estado Da Paraiba, Brazil. Because of its copper content, it has a bright and watery neon blue / green, also known as Paraiba color
According to the mineralogical name, "lithium tourmaline" is the most common variety, including pink to red, green to blue, colorless, yellow and mottled colors; and "magnesium tourmaline" is usually green and brown to black.
Factors affecting value
The color, clarity and transparency of tourmaline all affect its value, but the most important factor is color. Generally speaking, the value of palaiba tourmaline is much higher than that of other tourmaline varieties, followed by red tourmaline, blue tourmaline, pink and green watermelon tourmaline.
Wearing and preservation
"Tourmaline" is a gem with good durability, hardness of 7-7.5, good stability and toughness. For polychrome tourmaline, the junction of different colors is relatively fragile. Avoid high temperature heating, which may cause discoloration of tourmaline. There are some risks in sauna and ultrasonic cleaning.
It is best to use warm soapy water when cleaning.
More about the composition and crystal of tourmaline
The chemical formula of tourmaline is ab3c6 [x3y| (BO3) 3| si6o18], and the ions at a / B / C / X / y position are different in different tourmaline types. The most common elements include Al (aluminum), Mg (magnesium), Fe (iron), etc.
Tourmaline belongs to the trilateral crystal system. The crystal is in the shape of a column. Its cross-section can be trilateral, hexagonal or nine sided. The crystal surface of the trilateral is often raised, so the cross-section is a round triangle. Crystals are often long and multi striped, often accompanied by third-order symmetry, often parallel growth.
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