Topaz
Hardness 8 specific gravity 3.5-3.6
Refractive index 1.61-1.64 birefringence 0.008-10
Wear: good durability
Topaz is also known as topaz. Its chemical composition is Al2 (F, oh) 2sio4 (alfluorosilicate). As a natural gem, the most common color is yellow. At present, most of the Blue Topaz on the market are colored by irradiation.
Topaz is a November Birthstone.
The history of human understanding of topaz
The name "Topaz" comes from the Greek word "topazios", which is the ancient name of St. John's, a gem producing island in the Red Sea that is hard to find. However, it is said that the island produces not what we call "Topaz", but "chrysolite".
In the middle ages, people used "Topaz" to describe all the Yellow gemstones, and it was believed that it could strengthen the mind and avoid mental illness.
It wasn't until 1737 that German gemologists officially identified Topaz as the kind of gem we currently refer to.
Color and variety of topaz
In Gemmology, "Topaz" can be divided into "F type" and "Oh type". The chemical formula of "F type" is "al2f2sio4", and the chemical formula of "Oh type" is "Al2O3 2sio4".
The color of "type F" is usually yellow and does not show orange color. The name "Topaz" comes from it. Other colors include colorless, brown, blue, light green, etc.
The color of "Oh type" includes yellow, orange, pink and purple. Topaz, known as "imperial Topaz", is a kind of "Sherry" with orange hue in yellow. It is considered as the topaz of the highest grade.
The "Oh type" has light resistance, while the "F type" has a color other than blue, which will fade slowly when exposed to light.
Production and origin of topaz
"Topaz" is produced from pegmatite. Brazil is the main origin. Other origins include Australia, Japan, Madagascar, Mexico, Myanmar, Nigeria, Pakistan, Russia, Sri Lanka, the United States and Zimbabwe.
The main producing areas of "Oh type" are Brazil and Pakistan.
Common optimization processing
"Heating" - most of the pink "Topaz" comes from the heat treatment of yellow / Brown gemstones containing "chromium". It is believed that yellow is removed in the treatment process, leaving behind the "Chrome" caused by pink.
"Irradiation" - colorless Topaz can turn yellow and brown after irradiation, but these colors are unstable and will fade in the first place when exposed to light. After irradiation, heat treatment can be carried out on the gem to obtain stable blue color of various colors. This "irradiated and heated Blue Topaz has light resistance".
Factors affecting value
The "emperor Topaz" with orange body color and pink color is the most expensive, the untreated yellow and blue are equivalent, and the irradiated blue topaz is the least valuable.
Wearing and preservation
The hardness of "Topaz" is up to 8, so it will not be worn by dust in the air. However, due to the complete cleavage of "Topaz", it needs to be very careful in the cutting process, and collision should be avoided in daily wear.
For F-type topaz, it is necessary to avoid direct sunlight. However, the color of Blue Topaz heated by irradiation is very stable, and there is no need to worry about the light.
Avoid ultrasonic cleaning, steam, impact and instantaneous temperature difference.
It can be washed with warm soapy water.
Crystal habit of topaz
"Topaz" is a "rhombic system", a biaxial crystal, mainly in the form of rhombic columns, with a cross-section usually of diamond shape and complete cleavage in the direction parallel to the bottom axis.
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