All about Gemstones hardeness and qualities

Mohs  scale of Gemstones Hardness

When you are purchasing a gem for jewelry use one of the important considerations is the durability of that specific gemstone. One of the main measures of durability in gems is the “Mohs hardness” which is a scale developed by Freidrich Mohs in 1812.

In general terms a gem of 7 or greater hardness is considered suitable for ring wear because it is as hard or harder than quartz which is one of the most common forms of “dust” that the gem might encounter. Thus if the gemstone is as hard or harder than quartz it is unlikely to scratch easily with common dust rubbing against it. For engagement rings a hardness of 8 or greater is usually recommended for added durability since the gem will likely be worn daily.

Softer gems are often put in pendants where they run less risk of bumping into something and becoming damaged. Some designers also put them in rings, taking extra care in the design to protect the gem as much as possible and also cautioning their customers about care in wearing their ring. To protect your gem it is best to avoid things such as gardening, dish washing, remodeling and other more strenuous forms of activity while wearing your rings. In most cases this simple care will keep them beautiful for the next generation to enjoy.
Here is a table of common gemstones and their Mohs hardness to give you an idea of how this hardness scale works.

Moh's-table-of-precious-gems-hardness

 

It is interesting to note that the Mohs scale is not linear

IE a gem of 8 in hardness is not twice as hard as one of 4 in hardness. In most cases (especially at the upper end of the scale) each step up the mohs scale means a much greater hardness. Topaz at 8 on the Mohs scale for example is two times as hard as quartz which is a 7 on the scale.

Other factors also come into play when considering gemstone durability, such as whether or not the gem has distinct cleavage. “Cleavage” in gemstones is a weakness in one or more directions of the crystal that can allow the gem to cleave or “split” if struck just right. This is why some movies show diamonds being “struck” to split them. If you would like further information about the durability of a gem you are considering please.

 

Red Cushion cut Ruby

Ruby Gemstone

THE PRECIOUS GEMSTONE RUBY

Ruby is distinguished for its bright red color, being the most famed and fabled red gemstone. Beside for its bright color, it is a most desirable gem due to its hardness, durability, luster, and rarity. Transparent rubies of large sizes are even rarer than Diamonds. Ruby is the red variety of the mineral Corundum. Sapphire, the other gem variety of Corundum, encompasses all colors of Corundum aside from red. In essence, Ruby is a red Sapphire, since Ruby and Sapphire are identical in all properties except for color. However, because of the special allure and historical significance, Ruby has always been classified as an individual gemstone, and is never identified as a form of Sapphire (though some purplish-red colors may straddle the line of being classified as either Ruby or Sapphire).

About Rubies:

The color of Ruby ranges from bright red to dark reddish-brown. The most preferred color is a deep blood red with a slightly bluish hue. Such Ruby is known as “Burmse Ruby” or “Pigeon’s Blood Ruby”. Ruby from Burma is famous for its exceptional coloring, and has traditionally produced the finest Rubies. However, Burmese Ruby rarely exceeds several carats; large flawless Burmese Rubies can be worth millions of dollars. Many Rubies on the market are from Thailand, and these Rubies have a less-desirable
brownish hue, though they often can be heat treated  to improve color. Heat-treating a Ruby can also increase its transparency by removing tiny internal flaws.

Inclusions of tiny, slender, parallel Rutile needles in Ruby cause a polished gem to exhibit asterism. A Ruby displaying asterism is known as a “Star Ruby”, and if transparent can be very highly prized. Star Rubies exists in six ray stars, though twelve ray stars are also known. Rubies must be have good transparency to possess gem value. Opaque or semi-opaque Rubies have relatively little value, even if they display asterism.

The same Rutile inclusions that are responsible for asterism in certain Rubies can also decrease transparency and cause a hazy effect known as silk. Though Ruby can be one the most expensive gemstones, it also comes in more dull opaque forms that are fairly inexpensive, and are often polished into cabochons. A unique gemstone form composed of opaque red Ruby in contrasting green Zoisite is well known from Tanzania, and is used as a minor gemstone and can be carved into ornaments.

The color of Ruby is usually caused by minute inclusions of the metal chromium. These impurities are often responsible for causing a Ruby to fluorescent, which can be helpful in its identification. Ruby is also pleochroic, and will sometimes display a lighter and more intense color when viewed at different angles.

Ruby is a tough and durable gem, and the only natural gemstone harder than Ruby is Diamond. Despite this, Ruby is still subject to chipping and fracture if handled roughly, and care should be taken to ensure it is properly handled.

Ruby was first synthesized in 1902. The process of creating synthetic Ruby is known as the Verneuil process. Only experts can distinguish between natural and synthetic, lab-created Ruby.

Use of Rubies:

Ruby is the birthstone for July.

Ruby is one of the most popular gemstones, and is used extensively in Jewelry. Ruby is used in all forms of jewelry, including bracelets, necklaces, rings, and earrings. It is used both as centerpiece gemstone in pendants and rings, as well as a secondary stone to complement other gemstones such as Diamonds. Star Ruby is polished as cabochons, and, if clear, can be extremely valuable.

Large Ruby gems are extremely rare and valuable. Fine colored Ruby with a deep red color and excellent transparency can reach several thousand dollars a carat. Synthetic Rubies are inexpensive and often used as a cheap substitute for natural rubies.

Ruby types:

  • Burma Ruby  –   Ruby from Burma; synonym of Burmese Ruby.
  • Burmese Ruby  –  Ruby with an exceptional red color (usually but not necessarily from Burma). Occasionally also used to describe synthetic Ruby.
  • Pigeon’s Blood Ruby  –   Highly-desirable form of Ruby of a blood-red color with a hint of blue.
  • Ruby Fuschite  –  Describes a dark red Ruby in a green Fuschite mica matrix found in India.
  • Ruby Zoisite  –   Mixture of opaque red Ruby in green Zoisite from Tanzania. Ruby Zoisite has pretty contrast and is used as a minor gemstone, being polished into cabochons and carved into ornamental figures.

Star Ruby  –  Well-known form of Ruby

by displaying asterism, most often in the form of a six-rayed star.

 

Picture of Blue Sapphire

Hardness 9

 

THE PRECIOUS GEMSTONE SAPPHIRE

Sapphire is the birthstone of September.

Sapphire is the most precious and valuable blue gemstone. It is a very desirable gemstone due to its excellent color, hardness, durability, and luster. In the gem trade, Sapphire without any color prefix refers to the blue variety of the mineral Corundum. However, the term Sapphire encompasses all other gem varieties and colors of Corundum as well, excluding Ruby, the red variety of Corundum, which has its own name since antiquity.

Chemical Formula Al2O3
Color White, Colorless, Blue, Green, Yellow, Orange, Brown, Pink, Purple, Gray, Black, Multicolored
Hardness 9
Crystal System Hexagonal
Refractive Index 1.76 – 1.77

About Sapphire genstones:

The most valuable color of Sapphire is a cornflower blue color, known as Kashmir Sapphire or Cornflower Blue Sapphire. Another extremely valuable Sapphire form is the very rare, orange-pink Padparadschah. An exotic type of sapphire, known as C

lor Changing Sapphire, displays a different color depending on its lighting. In natural light, Color Changing Sapphire is blue, but in artificial light, it is violet. (This effect is the same phenomenon well-known in the gemstone Alexandrite). Yellow and pink Sapphire have recently become very popular, and are now often seen in jewelry.

Going way back in time, Sapphires (excluding blue) were often called the same name as a popular gemstone of that color with the prefix “oriental” added to it. For example, green Sapphire was called “Oriental Emerald”. The practice of applying the name of a different gemstone to identify the sapphire was misleading, and these names are no longer used. What was once called “Oriental Emerald” is now called “Green Sapphire”. The same holds true for all other color varieties of Sapphire. However, the word “Sapphire” in its plain context refers only to blue Sapphire, unless a prefix color is specified. Sapphire with a color other than blue is often called a “fancy” in the gem trade.

Sapphire often contains minor inclusions of tiny slender Rutile needles. When present, these inclusions decrease the transparency of a stone and are known as silk. When in dense, parallel groupings, these inclusions can actually enhance by allowing polished Sapphires to exhibit astersm. Sapphire gems displaying asterism are known as “Star Sapphire”, and these can be highly prized. Star Sapphire exists in six ray stars, though twelve ray stars are also known.

Sapphire is pleochroic, displaying a lighter and more intense color when viewed at different angles. Some pleochroic Sapphire is blue when viewed at one angle, and purple at a different angle. Color zoning, which forms from growth layers that build up during the formation of the stone, may also be present in certain Sapphires. Color zoning is responsible for certain Sapphires having lighter and darker colors in different parts of a crystal. Some Sapphire gemstones may even be multicolored such as purple and blue.

Sapphire is a tough and durable gem, and the only natural gemstone harder than Sapphire is Diamond. Despite this, Sapphire is still subject to chipping and fracture if handled roughly, and care should be taken to ensure it is properly handled. Sapphire was first synthesized in 1902. The process of creating synthetic Sapphire is known as the Verneuil process. Only experts can distinguish between natural and synthetic Sapphire.

Uses of Sapphire gemstones:

Sapphire is one of the most popular gemstones, and is used extensively in Jewelry. Fine colored Sapphire with a deep blue color and excellent transparency can reach several thousand dollars a carat. The blue variety is most often used in jewelry, but the yellow, pink, and orange “fancies have recently become very popular. Green and light blue Sapphires are also known, but are less commonly used in jewelry. Opaque Black Sapphire is also used a minor gemstone.

Sapphire is used in all forms of jewelry, including bracelets, necklaces, rings, and earrings. It is used both as centerpiece gemstone in pendants and rings, as well as a secondary stone to complement other gemstones such as Diamonds. Star Sapphires are polished as cabochons, and, if clear, are extremely valuable.

The rare orange-pink variety, known as Padparadschah, can be even more valuable than fine blue Sapphire. Blue Sapphire is sometimes carved into cameos or small figures, especially the less transparent material. Synthetic Sapphire is often used as a cheap substitute for the natural material.

Sapphire names:

Besides for the varieties of Sapphire listed below, Sapphire with color other than blue are prefixed with their color names. The main gemstone colors in addition to blue Sapphire include:
– Yellow Sapphire (sometimes also called “Golden Sapphire” if intensely colored)
– Pink Sapphire
– White Sapphire (describes Sapphire that is colorless)
– Green Sapphire
– Purple Sapphire
– Orange Sapphire
– Black Sapphire

  • Color-Change Sapphire  –   Sapphire that exhibits a different color in natural and artificial light.
  • Cornflower Blue Sapphire  –  Describing Sapphire with a cornflower-blue color, which can be better described as an intense, velvety-blue color. This term is often used in conjunction with Kashmir Sapphire to describe the Sapphire of that region, but it can also be used to describe any Sapphire with such color. Cornflower blue is the most desirable color in a Sapphire.
  • Fancy Sapphire  –   Describing any Sapphire with a color other than blue.
  • Kashmir Sapphire  –  Sapphire with an intense, velvety-blue color, described from the Kashmir Province of India. Kashmir Sapphire is considered to have the finest color of all Sapphire.
  • Padparadschah  –   Orange-pink variety of Sapphire that is found in Sri Lanka; highly regarded and one of the most valuable forms of Sapphire.

Star Sapphire  –  Well-known form of Sapphire displaying asterism in the form of a distinct, six-rayed star. Of all the gemstones that display asterism, Star Sapphire is most highly regarded and well-known.

 

SAPPHIRE TREATMENTS AND ENHANCEMENTS:

Sapphire is usually heat treated to intensify the blue color, as well as remove inclusions to increase clarity. It is standard industry practice to heat treat Sapphire gemstones, and most Sapphires used as gemstones have been heat treated. Sapphire with a natural, unheated color is much more valuable then the heat treated material, and gemstones of good quality can be extremely costly. Sapphires are sometimes colored through diffusion treatment, which artificially alters the color of the original gemstone. Diffused Sapphires colors include deep blue, bright yellow, bright orange and orange-red. The diffusion is often done by heat treating a stone in a beryllium metal overlay. Diffused Sapphire gemstones are fairly inexpensive despite their desirable color. Because of all the color treatments and enhancements performed to Sapphire gemstones, this information should always be fully disclosed to the buyer, and Sapphire should only be purchased from highly reputable dealers.

 

 

 

Beryl, emerald, 5.03 ct.

Beryl, emerald, 5.03 ct.

THE PRECIOUS GEMSTONE EMERALD

Emerald, the green variety of Beryl, is the most famous and valuable green gemstone. Its beautiful green color, combined with durability and rarity, make it one of the most expensive gemstones. Deep green is the most desired color in Emeralds. In general the paler the color of an Emerald, the lesser its value. Very pale colored stones are not called Emeralds but rather “Green Beryl”. They are sometimes heat treated, which causes their color to turn blue and transform into Aquamarine.

Chemical Formula Be3Al2SiO6
Color Green
Hardness 7.5 – 8
Crystal System Hexagonal
Refractive Index 1.57 – 1.58
SG 2.6 – 2.8
Transparency Transparent to translucent
Double Refraction .006
Luster Vitreous
Cleavage 3,1 – basal
Mineral Class Beryl (Emerald)

All about the gemstone Emerald:

Emerald is the birthstone of May

Besides for Emerald, the mineral Beryl also has other important gem varieties, including blue Aquamarine, pink Moranite, and yellow Heliodor/Golden Beryl Pure Beryl is white; the green color of Emerald is usually caused by chromium impurities, and occasionally by vanadium impurities. Emerald is by far the most valuable gemstone variety of Beryl, being one of the few precious gemstones.

Emeralds are notorious for their flaws. Flawless stones are very uncommon, and are noted for their great value. Some actually prefer Emeralds with minute flaws over flawless Emeralds, as this proves authenticity. Flaws are often hidden by treating the Emeralds with oil or synthetic lubricants, and this is a common practice in the industry. Though Colombian Emeralds have traditionally been the highest quality Emeralds with the finest green color, a new source of Emerald from the African country of Zambia has been producing deep green Emeralds with fewer flaws.

Many Emerald fakes and doublets are known. Two pale colored stones may be glued together with a deep green paste, creating a stone resembling Emerald. Faceted green glass also resembles Emerald, and it may be coated with a hard substance to mask its low hardness. Synthetic Emeralds are also sold to unwary buyers without them knowing the stone is synthetic. Experts can distinguish all these fakes, and it is especially important to only purchase Emeralds from reliable dealers. Experts can also determine if an Emerald was treated with oil or a lubricant to mask internalflaws.

A rare and unusual form of Emerald, known as “Trapiche Emerald”, is characterized by star-shaped rays that emanate from the center of a stone in a hexagonal pattern. These rays appear much like asterism, but, unlike asterism, are not caused by light reflection from tiny parallel inclusions, but by black carbon impurities that form in a star-shaped pattern. These Trapiche Emeralds are only found in the Boyaca Emerald mining district of Colombia, and are cut into cabochons.

Though Emerald has good hardness, it is a brittle stone. It may develop internal cracks if banged hard or if subject to extreme temperature change. Emeralds that were treated to mask internal flaws should never be cleaned with an ultrasonic jewelry cleaner, nor should they be washed with soap. These practices may remove the oiling treatment and expose the hidden internal flaws.

 

USES of the gemstone Emerald

Transparent emeralds are faceted into gem cuts for jewelry, and make one of the most popular jewelry gemstones. Emerald is very sensitive to pressure and banging, and the well-known emerald cut was developed specifically for this gem to reduce the amount of pressure during cutting. Translucent Emeralds are cut and polished into cabochons and beads, as are Trapiche Emeralds.

.Emerald gemstone names:

  • Brazilian Emerald  –   Emerald from Brazil. The term Brazilian Emerald may also refer to green Tourmaline from Brazil.
  • Cat’s Eye Emerald  –  Emerald exhibiting cat’s eye effect. Cat’s eye emerald is very rare, and only exists on paler Emeralds.
  • Colombian Emerald  –   Emerald from Colombia. This Emerald is usually regarded as the highest quality.
  • Star Emerald  –  Synonym of Trapiche Emerald.
  • Trapiche Emerald  –   Emerald with black impurities in the form of a six-rayed star.

Zambian Emerald  –  Emerald from the African country of Zambia. Zambian Emeralds can have very good color and transparency.

 

Emerald gemstones Treatments and Enhancements:

Emerald flaws are very often concealed by treating a stone with oil or synthetic lubricants. This is a common practice in the gemstone industry. The fracture-filling materials contain very similar refractive indices to the Emerald, optically hiding the underlying flaw. Oiling is preformed by heating the Emeralds in a cylinder containing the oil, which allows it to penetrate through the heat. Though the oiling procedure is most frequently performed with cedar oil, newer, more effective fracture-filling techniques are being practiced, including irradiation. One should always inquire aboutoiling and fracture filling when purchasing an Emerald, as these techniques will affect the price of a gemstone. Generally, unless otherwise specified, it can be assumed that an Emerald has been oiled or otherwise fracture-filled. Standard oiling procedures are also not permanent, and the oiling may slowly wear off naturally, though frequent cleaning can hasten this process.

This entry was posted in Gem stones and tagged . Bookmark the permalink.