What is a gemstone ?

 

*Text rom Wikipedia, photos from Mauro Pantò

 

A gemstone or gem (also called a precious or semi-precious stone, a fine gem, or jewel) is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments.[1][2] However certain rocks, (such as lapis lazuli) and organic materials (such as amber or jet) are not minerals, but are still used for jewelry, and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their lustre or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone. Apart from jewelry, from earliest antiquity until the 19th century engraved gems and hardstone carvings such as cups were major luxury art forms; the carvings of Carl Fabergé were the last significant works in this tradition.

 

 

Characteristics and classification

The traditional classification in the West, which goes back to the Ancient Greeks, begins with a distinction between precious and semi-precious stones; similar distinctions are made in other cultures. In modern usage the precious stones are diamond, ruby, sapphire and emerald, with all other gemstones being semi-precious.[3] This distinction reflects the rarity of the respective stones in ancient times, as well as their quality: all are translucent with fine color in their purest forms, except for the colorless diamond, and very hard,[4] with hardnesses of 8–10 on the Mohs scale. Other stones are classified by their color, translucency and hardness. The traditional distinction does not necessarily reflect modern values, for example, while garnets are relatively inexpensive, a green garnet called Tsavorite, can be far more valuable than a mid-quality emerald.[5] Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone. Use of the terms ‘precious’ and ‘semi-precious’ in a commercial context is, arguably, misleading in that it deceptively implies certain stones are intrinsically more valuable than others, which is not the case.

In modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition. For example, diamonds are made of carbon (C) and rubies of aluminium oxide (Al2O3). Next, many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic. Another term used is habit, the form the gem is usually found in. For example diamonds, which have a cubic crystal system, are often found as octahedrons.

Gemstones are classified into different groups, species, and varieties. For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Emerald (green), aquamarine (blue), red beryl (red), goshenite (colorless), heliodor (yellow), and morganite (pink) are all varieties of the mineral species beryl.

Gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and luster. They may exhibit pleochroism or double refraction. They may have luminescence and a distinctive absorption spectrum.

Material or flaws within a stone may be present as inclusions.

Gemstones may also be classified in terms of their “water”. This is a recognized grading of the gem’s luster and/or transparency and/or “brilliance”.[6] Very transparent gems are considered “first water“, while “second” or “third water” gems are those of a lesser transparency.[7]

 

 

Value

There is no universally accepted grading system for gemstones. Diamonds are graded using a system developed by the Gemological Institute of America (GIA) in the early 1950s. Historically, all gemstones were graded using the naked eye. The GIA system included a major innovation: the introduction of 10x magnification as the standard for grading clarity. Other gemstones are still graded using the naked eye (assuming 20/20 vision).[8]

A mnemonic device, the “four Cs” (color, cut, clarity and carats), has been introduced to help the consumer understand the factors used to grade a diamond.[9] With modification, these categories can be useful in understanding the grading of all gemstones. The four criteria carry different weight depending upon whether they are applied to colored gemstones or to colorless diamond. In diamonds, cut is the primary determinant of value, followed by clarity and color. Diamonds are meant to sparkle, to break down light into its constituent rainbow colors (dispersion), chop it up into bright little pieces (scintillation), and deliver it to the eye (brilliance). In its rough crystalline form, a diamond will do none of these things; it requires proper fashioning and this is called “cut”. In gemstones that have color, including colored diamonds, it is the purity and beauty of that color that is the primary determinant of quality.

Physical characteristics that make a colored stone valuable are color, clarity to a lesser extent (emeralds will always have a number of inclusions), cut, unusual optical phenomena within the stone such as color zoning, and asteria (star effects).

                                                                                color change star spinel

Color zoning is the uneven distribution of coloring within a gem. The Greeks, for example, greatly valued asteria in gemstones, which were regarded as a powerful love charm, and Helen of Troy was known to have worn star-corundum.[10]

Historically, gemstones were classified into precious stones and semi-precious stones. Because such a definition can change over time and vary with culture, it has always been a difficult matter to determine what constitutes precious stones.[11]

Aside from the diamond, the ruby, sapphire, emerald, pearl (strictly speaking not a gemstone) and opal[11] have also been considered to be precious. Up to the discoveries of bulk amethyst in Brazil in the 19th century, amethyst was considered a precious stone as well, going back to ancient Greece. Even in the last century certain stones such as aquamarine, peridot and cat’s eye have been popular and hence been regarded as precious.

  sillimanite cat’s eye

Nowadays such a distinction is no longer made by the trade.[12] Many gemstones are used in even the most   expensive jewelry, depending on the brand name of the designer, fashion trends, market supply, treatments, etc. Nevertheless, diamonds, rubies, sapphires and emeralds still have a reputation that exceeds those of other gemstones.

Rare or unusual gemstones, generally meant to include those gemstones which occur so infrequently in gem quality that they are scarcely known except to connoisseurs, include andalusite, axinite, cassiterite, clinohumite and red beryl.

 

 

 

 

tanzanite                                red beryl or bixbite                  tsavorite

Gem prices can fluctuate heavily (such as those of tanzanite over the years) or can be quite stable (such as those of diamonds). In general per carat prices of larger stones are higher than those of smaller stones, but popularity of certain sizes of stone can affect prices. Typically prices can range from 1USD/carat for a normal amethyst to US$20,000–50,000 for a collector’s three carat pigeon-blood almost “perfect” ruby.

Grading

In the last two decades[when?] there has been a proliferation of certification for gemstones. There are a number of[12] laboratories which grade and provide reports on diamonds.

  • International Gemological Institute (IGI), independent laboratory for grading and evaluation of diamonds, jewellery and colored stones.
  • Gemological Institute of America (GIA), the main provider of education services and diamond grading reports
  • Hoge Raad voor Diamant (HRD Antwerp), The Diamond High Council, Belgium is one of Europe’s oldest laboratories. Its main stakeholder is the Antwerp World Diamond Centre.
  • American Gemological Society (AGS) is not as widely recognized nor as old as the GIA.
  • American Gem Trade Laboratory which is part of the American Gem Trade Association (AGTA), a trade organization of jewelers and dealers of colored stones.
  • American Gemological Laboratories (AGL), which was sold by “Collector’s Universe” a NASDAQ listed company which specializes in certification of collectibles such as coins and stamps. It is now owned by Christopher P. Smith, who was awarded the Antonio C. Bonanno Award for Excellence in Gemology in 2009
  • European Gemological Laboratory (EGL), founded in 1974 by Guy Margel in Belgium.
  • Gemmological Association of All Japan (GAAJ-ZENHOKYO), Zenhokyo, Japan, active in gemological research
  • Gemmological Institute of Thailand (GIT) is closely related to Chulalongkorn University
  • Gemmology Institute of Southern Africa, Africa’s premium gem laboratory.
  • Asian Institute of Gemmological Sciences (AIGS), the oldest gemological institute in South East Asia, involved in gemological education and gem testing
  • Swiss Gemmological Institute (SSEF), founded by Prof. Henry Hänni, focusing on colored gemstones and the identification of natural pearls
  • Gübelin Gem Lab, the traditional Swiss lab founded by Dr. Eduard Gübelin. Their reports are widely considered as the ultimate judgement on high-end pearls, colored gemstones and diamonds.[citation needed]

Each laboratory has its own methodology to evaluate gemstones. Consequently a stone can be called “pink” by one lab while another lab calls it “Padparadscha”. One lab can conclude a stone is untreated, while another lab concludes that it is heat treated.[12] To minimise such differences, seven of the most respected labs, i.e. AGTA-GTL (New York), CISGEM (Milano), GAAJ-ZENHOKYO (Tokyo), GIA (Carlsbad), GIT (Bangkok), Gübelin (Lucerne) and SSEF (Basel), have established the Laboratory Manual Harmonisation Committee (LMHC), aiming at the standardization of wording on reports and certain analytical methods and interpretation of results. Country of origin has sometimes been difficult to find agreement on due to the constant discovery of new locations. Moreover determining a “country of origin” is much more difficult than determining other aspects of a gem (such as cut, clarity etc.).[13]

Gem dealers are aware of the differences between gem laboratories and will make use of the discrepancies to obtain the best possible certificate.[12]

Cutting and polishing

pre-forming gems in Bangkok

A few gemstones are used as gems in the crystal or other form in which they are found. Most however, are cut and polished for usage as jewelry. The picture to the left is of a rural, commercial cutting operation in Thailand. This small factory cuts thousands of carats of sapphire annually. The two main classifications are stones cut as smooth, dome shaped stones called cabochons, and stones which are cut with a faceting machine by polishing small flat windows called facets at regular intervals at exact angles.

faceting in Bangkok

Stones which are opaque such as opal, turquoise, variscite, etc. are commonly cut as cabochons. These gems are designed to show the stone’s color or surface properties as in opal and star sapphires. Grinding wheels and polishing agents are used to grind, shape and polish the smooth dome shape of the stones.[14]

 

my cabbing maching

 

 

 

 

Gems which are transparent are normally faceted, a method which shows the optical properties of the stone’s interior to its best advantage by maximizing reflected light which is perceived by the viewer as sparkle. There are many commonly used shapes   for   faceted stones.

  advanced faceting maching

The facets must be cut at the proper  angles, which varies depending on the optical properties of the gem. If the angles are too steep or too shallow, the light will pass through and not be reflected back toward the viewer. The faceting machine is used to hold the stone onto a flat lap for cutting and polishing the flat facets.[15] Rarely, some cutters use special curved laps to cut and polish curved facets.

Color

The color of any material is due to the nature of light itself. Daylight, often called white light, is actually a mixture of different colors of light. When light passes through a material, some of the light may be absorbed, while the rest passes through. The part that is not absorbed reaches the eye as white light minus the absorbed colors. A ruby appears red because it absorbs all the other colors of white light (blue, yellow, green, etc.) except red.

The same material can exhibit different colors. For example ruby and sapphire have the same chemical composition (both are corundum) but exhibit different colors. Even the same gemstone can occur in many different colors: sapphires show different shades of blue and pink and “fancy sapphires” exhibit a whole range of other colors from yellow to orange-pink, the latter called “Padparadscha sapphire”.

This difference in color is based on the atomic structure of the stone. Although the different stones formally have the same chemical composition, they are not exactly the same. Every now and then an atom is replaced by a completely different atom (and this could be as few as one in a million atoms). These so called impurities are sufficient to absorb certain colors and leave the other colors unaffected.

For example, beryl, which is colorless in its pure mineral form, becomes emerald with chromium impurities. If you add manganese instead of chromium, beryl becomes pink morganite. With iron, it becomes aquamarine.

Some gemstone treatments make use of the fact that these impurities can be “manipulated”, thus changing the color of the gem.

Treatment

Gemstones are often treated to enhance the color or clarity of the stone. Depending on the type and extent of treatment, they can affect the value of the stone. Some treatments are used widely because the resulting gem is stable, while others are not accepted most commonly because the gem color is unstable and may revert to the original tone.[16]

Heat

Heat can improve gemstone color or clarity. The heating process has been well known to gem miners and cutters for centuries, and in many stone types heating is a common practice. Most citrine is made by heating amethyst, and partial heating with a strong gradient results in ametrine—a stone partly amethyst and partly citrine. Much aquamarine is heated to remove yellow tones and change the green color into the more desirable blue or enhance its existing blue color to a purer blue.[17]

Nearly all tanzanite is heated at low temperatures to remove brown undertones and give a more desirable blue/purple color. A considerable portion of all sapphire and ruby is treated with a variety of heat treatments to improve both color and clarity.

When jewelry containing diamonds is heated (for repairs) the diamond should be protected with boracic acid; otherwise the diamond (which is pure carbon) could be burned on the surface or even burned completely up. When jewelry containing sapphires or rubies is heated, it should not be coated with boracic acid or any other substance, as this can etch the surface; they do not have to be “protected” like a diamond.

Radiation

Virtually all blue topaz, both the lighter and the darker blue shades such as “London” blue, has been irradiated to change the color from white to blue. Most greened quartz (Oro Verde) is also irradiated to achieve the yellow-green color.

  topaz-

before and after irradiation and heating- this special laser cut is my design

 

  

Waxing/oiling

Emeralds containing natural fissures are sometimes filled with wax or oil to disguise them. This wax or oil is also colored to make the emerald appear of better color as well as clarity. Turquoise is also commonly treated in a similar manner.

Fracture filling

Fracture filling has been in use with different gemstones such as diamonds, emeralds and sapphires. In 2006 “glass filled rubies” received publicity. Rubies over 10 carat (2 g) with large fractures were filled with lead glass, thus dramatically improving the appearance (of larger rubies in particular). Such treatments are fairly easy to detect.

UV short and long wave  may cause color change:

  

Willemite,Calcite and Franklinite, N.J.                                Tremolite, New York

Fluorescence and tenebrescence after exposure at 10 second of UV light.The purple color will stay for a couple of hours

   Hackmanite ,Burma

Color change due to different wave lenght

Cuprite, Mexico  -picture taken at daylight and incandescent light-

Synthetic and artificial gemstones

Some gemstones are manufactured to imitate other gemstones. For example, cubic zirconia is a synthetic diamond simulant composed of zirconium oxide. Moissanite, also a synthetic stone, is another example. The imitations copy the look and color of the real stone but possess neither their chemical nor physical characteristics. Moissanite actually has a higher refractive index than diamond and when presented beside an equivalently sized and cut diamond will have more “fire” than the diamond.

However, lab created gemstones are not imitations. For example, diamonds, ruby, sapphires and emeralds have been manufactured in labs to possess identical chemical and physical characteristics to the naturally occurring variety. Synthetic (lab created) corundums, including ruby and sapphire, are very common and they cost only a fraction of the natural stones. Smaller synthetic diamonds have been manufactured in large quantities as industrial abrasives, although larger gem-quality synthetic diamonds are becoming available in multiple carats.[18]

Whether a gemstone is a natural stone or a lab-created (synthetic) stone, the characteristics of each are the same. Lab-created stones tend to have a more vivid color to them, as impurities are not present in a lab and do not modify the clarity or color of the stone.

Notes

^ The Oxford Dictionary Online and Webster Online Dictionary

  1. ^ Alden, Nancy (2009). Simply Gemstones: Designs for Creating Beaded Gemstone Jewelry. New York: Random House. p. 136. ISBN 978-0-307-45135-4. Retrieved November, 3 2010.
  2. ^ Precious Stones, Max Bauer, p 2
  3. ^ Precious Gemstone glossary of Jewelry
  4. ^ Wise, R. W., 2006, Secrets Of The Gem Trade, The Connoisseur’s Guide To Precious Gemstones, Brunswick House Pr, pp. 3–8 ISBN 0972822380
  5. ^ AskOxford.com Concise Oxford English dictionary online.
  6. ^ Desirable diamonds: The world’s most famous gem. by Sarah Todd.
  7. ^ Wise, R. W., 2006, Secrets of The Gem Trade, The Connoisseur’s Guide To Precious Gemstones, Brunswick House Pr, p.36 ISBN 0972822380
  8. ^ Wise, R. W., 2006, Secrets Of The Gem Trade, The Connoisseur’s Guide To Precious Gemstones, Brunswick House Pr, p. 15
  9. ^ Burnham, S.M. (1868). Precious Stones in Nature, Art and Literature. Bradlee Whidden. Page 251 URL: Helen of Troy and star corundum
  10. ^ a b Church, A.H. (Professor at Royal Academy of Arts in London) (1905). Precious Stones considered in their scientific and artistic relations. His Majesty’s Stationary Office, Wyman & Sons. Chapter 1, Page 9: Definition of Precious Stones URL: Definition of Precious Stones
  11. ^ a b c d Secrets of the Gem Trade; The Connoisseur’s Guide to Precious Gemstones Richard W Wise, Brunswick House Press, Lenox, Massachutes., 2003
  12. ^ “Rapaport report of ICA Gemstone Conferene in Dubai”. Diamonds.net. 2007-05-16. Retrieved 2010-07-30.
  13. ^ Introduction to Lapidary by Pansy D. Kraus
  14. ^ Faceting For Amateurs by Glen and Martha Vargas
  15. ^ Gemstone Enhancement: History, Science and State of the Art by Kurt Nassau
  16. ^ Nassau, Kurt (1994). Gem Enhancements. Butterworth Heineman.
  17. ^ “New Process Promises Bigger, Better Diamond Crystals”. Carnegie Institution for Science. Retrieved 7 January 2011.

……..………………………………………………………..§………………………………………………………………….

Personal note- by  Mauro Pantò

Gems in ancient times-

When the man started to being attracted by gems or minerals? And why he use gems as ornaments?

  • I think that our ancestors first of all they were looking for hard stones such as flint, agate and obsidian as they can be fashioned into tools , spears,drills, arrowhead or knifes. Probably the way to carring these tools around, was a simple leather bag or a threads around the tool,either for a scraper or a spear point.The second step comes naturally to hang the items on his neck: it was the simplest ad efficient way to carry. Further more a man with a bigger or more shining or colorful tools attracted the respectability from the whole tribe and ,why not… from the females.From that point on, the second step arise: MAGICK.
  •  

 

 

 

 

 

lybian glass scraper

  • Special sensitve men as sciamans or tribe chief were considered with more respect if they had the power to call or dominate spirits, and the use of certain stones in order to perform rituals, were a must.Therefore , without investigate their beliefe, special gems or stones with magic attribute were the key to control the entire society, visible or invisible.
  • The stones of the Hoshen      

The brestplate covered with 12 stones first worn the High Priest Aaron,brother of Moshe was the most famous old jewels who act as intermediary between the 12 tribes and God.The gemstones represent the perfection of nature and the aspiration of man.

The twelve stones symbolise the unity of the Jewish people and their equal status before the Almighty. As precious and nonprecious stones were set together in the Hoshen, so too are the nobleborn and the commoner all equal before God.

The 12 stones of Hoshen are:

Carnellian: Reuven symbol of love and marriage; aids conception, pregnancy and birth

Topaz: Shimon brings blessing of joy and abundance to your life

Emerald Levi symbol of generosity, modesty and kindness

Turquoise Yehuda leads to success in business affairs

Lapis lazuli Yissachar symbol of honesty and clarity of thought

Quartz Zevulun bestows strength; symbolises purity and the love of truth

Jacinth(zircon) Dan stimulates creativity; brings on to silf-fulfillment

Agate Naphtali has a special calming effect

Amethyst Gad symbol of spiritual strength; guards against negative energies

Chrysolite Asher purifies both body and soul; brings inner peace

Onyx Yosef strengthens one’s courage and self-control

Jasper Binyamin bestows physical strength; raises self-esteem

 

sassanid intaglio seal    2° to 6° Cent. A.D.

indo valley beads dated around 2° -3° millenium B.C. ( the gold is new )

- Gems during Greek-Roman empire-

Carnellian,jasper or chalcedony were the most common stones in use as jewelry for the Greek and Romans.Great value was given to engraved figures as intaglios and cameos. Only rich personality could afford to buy such things. Higher quality details were demand high price.Mostly were personal seals with emperors face or goddess/heroes engraved. Beads of agates and jasper were also made. In the roman time there was not much enfasis regading properties or specific magical attribute, but a big change occur a thousand year later.

- Gems in the middle-age

During this period the science of the earth and science of the Divine world were one. There was no separation and a Philosopher was a man of Knowledge. Alchemy and mathematic or fisic were married together with Kabbalah /Qabbalàh and Astrology.Therefore the whole world of matter and spirit was unity of forces and energy linked together.( pre-quantic era?). In this effort to understand the connection between spirit and matter,the gems played an important role. “De Occulta Philosophia” written in the 14° Century by Enrico Cornelio Agrippa ( Henri Carneille Agrippa),is a book of macick and science,typical of that age.In this book there is a clear description of the gems linked to planets ,days,plants,numbers,natural elements and all connected to the spiritual world .A simple correlation:

Sun: topaz,chrysoprase,orpimet

Moon: quartz ,selenite,pearl

Saturn: carnellian,sapphire,jasper

Jupiter: beryl,sapphire,emerald

Mars: diamond,amethyst

Venus: chrisolite,emerald

Mercury: agate,opal

There is much more in all books of that period and often the truth is mixed with superstition and simbology.The key to reveal the hidden knowledge is in the clean heart of the searcher.

Many other famous authors has written about gems powers, during middle -age and further more in reinassance period.

  • Gems in the 17°-18° Century

In this period there was an improvement of understanding the quality and physical property of gems. Also the skill of cutting and polishing made an important step,especially in Idar Oberstein ,Germany. While in the past the gems were simple rounded with poor polish,now the new technology was the key to reach important result in the cutting and faceting gems. Since then many steps has been made and today the cutters have reach the perfection.

  • Gems today

Gemology ( science that study gems property ) has made giant steps: now we can understand deeply a gem composition,it’s phisical and optical properties,we can look inside the atomic bonds,we can change it’s colors with irradiation and heat,we can create syntetic gems , like growing flowers..and with the new cutting machines we can reach absolute level of perfection. Jewellers can benefit of all this and so the consumers,but remain a question: why a person prefer pay a fortune for a real gem instead of buying a cheap imitation?

I believe that beside the logical common sense of investement ( you can carry with you a million $ on a ring..) there is a inconscious reason: energy.We want to feel and capture a natural energy that is trapped inside this misterious thing we call… GEM.

© Mauro Pantò 9 December 2011

Leave a Comment

*

*