[edit] Hardness (Vickers)

Comparison between Hardness (Mohs) and Hardness (Vickers):^[14]

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.

There are over 130 species of minerals that have been cut into gemstones with 50 species in common use. These include:

• Agate
• Alexandrite and other varieties of chrysoberyl
• Aquamarine and other varieties of beryl
• Chrysocolla
• Chrysoprase
• Diamond
• Emerald
• Feldspar (moonstone)
• Garnet
• Hematite
• Jade - jadeite and nephrite
• Jasper
• Kunzite
• Lapis lazuli
• Malachite
• Obsidian
• Olivine (Peridot)
• Opal (Girasol)
• Pyrite
• Quartz and its varieties
  • Agate
  • Amethyst (cardinal gem)
  • Citrine
  • Chalcedony (bloodstone)
  • Onyx
  • Tiger's-eye
• Ruby
• Sapphire dark blue
• Spinel
• Sugilite
• Tanzanite and other varieties of zoisite
• Topaz
• Turquoise
• Tourmaline
• Variscite
• Zircon

[edit] Artificial and synthetic

Artificial or synthetic materials used as gems include:

• High-lead glass
• Synthetic corundum
• Synthetic cubic zirconia

spinel

• Synthetic moissanite

[edit] Organic

There are a number of organic materials used as gems, including:

• Amber
• Ammolite - from fossils formed from the shells of extinct ammonites.
• Bone
• Coral
• Ivory
• Jet (lignite)
• Nacre (Mother of pearl)
• Pearl

[edit] Rare

Minerals that infrequently occur in gem quality form:

• Andalusite
• Axinite
• Benitoite
• Bixbite (Red beryl)
• Cassiterite
• Clinohumite
• Iolite
• Onyx
• Kornerupine
• Natural moissanite
• Zeolite (Thomsonite)

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".Very transparent gems are considered "first water", while "second" or "third water" gems are those of a lesser transparency.

Value of gemstones

Jewelry made with amber



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).

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. 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). 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.



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, Aside from the diamond, the ruby, sapphire, emerald, pearl (strictly speaking not a gemstone) and opal 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.

Nowadays such a distinction is no longer made by the trade. 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.

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 20,000-50,000USD for a collector's three carat pigeon-blood almost "perfect" ruby.

Grading

Enamelled gold, amethyst and pearl pendant, about 1880, Pasquale Novissimo (1844–1914), V&A Museum number M.36-1928.

In the last two decades[when?] there has been a proliferation of certification for gemstones. There are a number of 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) Gem dealers are aware of the differences between gem laboratories and will make use of the discrepancies to obtain the best possible certificate. Cutting and polishing

Raw gemstones. A rural Thai gem cutter

.

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.

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.

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. 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. Rarely, some cutters use special curved laps to cut and polish curved facets.

Gemstone color

Color is the most obvious and attractive feature of gemstones. 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.

Treatments applied to gemstones

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.

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.

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

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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. 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.

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 is another example, although it is a gemstone in its own right. 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

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.

Hybrid gemstones

The terms synthetic, natural, artificial, and imitation are well-understood by gemologists. However, gemologists have had to continually explain these terms, as applied in gemology, both to those within and outside of the industry, as synthetic in particular has different definitions when applied to different fields.

It is precisely because certain new gem treatments overlap more than one gem category that the term hybrid has been suggested. These materials consist of an original natural material that has been significantly added to – to the extent that the term natural no longer applies. Hybrid gems consist of natural material along with artificial material – either synthetic growth or polymers or glasses.

Hybrid is defined as those gem materials where there is no easy means of separating the natural from the artificial components. This is key, in that with a doublet or a triplet, the natural material can be isolated, identified – and theoretically retrieved from the whole. Hybrid will not be confused with assembled, but it will encompass reconstructed materials as well as B-jades.

Hybrid will not apply to traditional oiling of emerald and (comparatively minor) fracture healing as seen in many Mong Hsu rubies; these treatments are insignificant in comparison and additives would account for less than 5% of the total mass in most cases, but there remains the possibility that some heavily treated stones in these categories may qualify as hybrids.

Major industry educators, dealers, and trade organizations have seen the need for this new upper-level category. In some ways it is a dramatic addition to the gemological terms, but is merely a natural evolution due to modern treatment methods.

List of famous gemstones

A number of gemstones have gained fame because of their size and beauty or because of the people who owned or wore them. A partial list of famous gemstones follows.

Aquamarines

• The Giant Aquamarine

Diamonds

• The Allnatt Diamond
• The Centenary Diamond
• The Cullinan Diamond, the largest rough gem-quality diamond ever found at 3106.75 carats, also known as the Star of Africa
• The Darya-ye Noor Diamond, the best known diamond of the Iranian Crown Jewels
• The Deepdene
• The Dresden Green Diamond
• The Dudley Diamond
• The Eugenie Blue Diamond
• The Excelsior Diamond
• The Florentine Diamond
• The Golden Jubilee (the largest faceted diamond ever cut, at 545.67 carats)
• The Great Chrysanthemum Diamond
• The Great Mogul Diamond
• The Heart of Eternity Diamond (perhaps the largest Fancy Vivid Blue)
• The Hope Diamond (blue, but supposedly cursed)
• The Hortensia Diamond
• The Idol's Eye
• The Incomparable Diamond
• The Jones Diamond
• The Koh-i-Noor (a very old diamond, mentioned in Baburnama of 1526, is surrounded by legend and believed to be the most precious)
• The Millennium Star (the largest colorless, flawless diamond)
• The Moussaieff Red Diamond (the largest Fancy Vivid Red)
• The Nizam Diamond
• The Ocean Dream Diamond (the only known natural Fancy Deep Blue-Green)
• The Oppenheimer Diamond
• The Orloff (an Indian rose cut, rumored to have served as the eye of a Hindu statue)
• The Paragon Diamond
• The Portuguese Diamond
• The Premier Rose Diamond
• The Pumpkin Diamond (perhaps the largest Fancy Vivid Orange)
• The Red Cross Diamond
• The Regent Diamond
• The Sancy
• The Spirit of de Grisogono Diamond (the world's largest cut Black)
• The Star of the South
• The Steinmetz Pink Diamond (the largest Fancy Vivid Pink)
• The Taylor-Burton Diamond
• The Tiffany Yellow Diamond
• The Vargas

Emeralds

• The Duke of Devonshire
• The Gachala Emerald
• The Mackay Emerald

Opals

• The Andamooka Opal (presented to Queen Elizabeth 2, also known as the Queen's Opal)
• The Aurora Australis Opal (considered the most valuable black opal)
• The Black Prince Opal (originally known as Harlequin Prince)
• The Empress of Australia Opal
• The Fire Queen Opal
• The Flame Queen Opal
• The Flamingo Opal
• The Halley's Comet Opal (the world's largest uncut black opal)
• The Jupiter Five Opal
• The Olympic Australis Opal (reported to be the largest and most valuable gem opal ever found)
• The Pride of Australia Opal (also known as the Red Emperor Opal)
• The Red Admiral Opal (also known as the Butterfly Stone)

Ruby

• The DeLong Star Ruby
• The Hixon Ruby Crystal
• The Midnight Star Ruby
• The Neelanjali Ruby
• The Rajaratna Ruby
• The Rosser Reeves Ruby

Sapphires

• The Logan Sapphire
• The Queen Marie of Romania Sapphire
• The Ruspoli Sapphire
• The Star of Asia Star Sapphire
• The Star of Bombay (given to Mary Pickford by Douglas Fairbanks, Sr.)
• The Star of India (the world's largest and most famous star sapphire)
• The Stuart Sapphire

Spinels

• The Black Prince's Ruby (a spinel mounted on the Imperial State Crown)
• The Samarian Spinel (the world's largest spinel)
• The Timur Ruby (believed to be a ruby until 1851)

Topaz

• The American Golden Topaz (the largest cut yellow topaz, weighing nearly 23,000 carats)

See also

• List of minerals
• Lapidary
• Jewelry

References

• The Audubon Society Field Guide to North American Rocks and Minerals. 1978, New York, Alfred A. Knopf. ISBN 0394502698
• Hurlbut, Cornelius S.; Cornelius Klein. 1985. Manual of Mineralogy, 20th ed. New York: John Wiley and Sons. ISBN 0471805807
• Weinstein, Michael. 1958. The World of Jewel Stones. New York: Sheridan House.

External links

• The Mineral and Gemstone Kingdom
• USGS: Gemstones - Statistics and Information
• mindat.org: The Mineral and Location Database
• Misleading Gem Names
• Famous diamonds: 261 referred diamonds
• Diamonds in Conflict

  Difference Between Precious And Semiprecious

  Perhaps the most obvious sign of a lack of appreciation of gemstones is the common use of the term "semiprecious". While in a famous retail store GEMOLOGIST noticed a couple examining with obvious interest and appreciation an attractive brooch set with green stones. He overheard the man ask about the stones in the piece. The "salesman", if he could be called that, answered, "Oh, those are just semiprecious stones called tourmaline". The prospective customers, who had shown keen interest in the brooch, left the store immediately without looking at other merchandise. This example points up a practice that is all too common among jewelers.

  Almost every gem mineral is found and is for sale in the industry in a great variety of qualities. One quality of jade in a ten carat size may sell for $4 and another quality for $80 or much more. A ruby may be very fine and sell for $400 pet carat. A large opal may range in value from $4 to $1,000. Almost every variety of the transparent gem species may occur in gem quality and be properly called a precious stone from a relative price stand point, whereas another specimen of the same variety may be almost worthless. Not every ruby is precious and not every piece of jade is semiprecious. This is one reason for calling all stones GEMSTONES and not classifying them as precious and semiprecious. More important is the fact that the moment that we call stones semiprecious, we have lessened their value in the eyes of the general public, and the desirability and sale of many stones of great merit are thus substantially decreased.

  The most common query received by the jeweler from the customer who sees an unfamiliar stone seems to be "Is it a precious stone?" If the jeweler is not a student of colored stones, his probable answer is, "No, it is only a semiprecious one; diamond, ruby, sapphire and emerald (and perhaps he includes pearl) are the only precious stones. Every experienced gem salesman knows that this statement may have the result of immediately destroying in the customer's mind any interest whatever in the stone about which the inquirer was made and for which the inquirer may have been a customer. This is another of the reasons for the common belief that "colored stones don’t sell".

  Few Indians & Foreigners desire anything but the best. They don't have to have gems and jewelry, and unless they have a desired or need for a thing, they won't buy it unless high pressured. High pressure results in dissatisfied customers. Semiprecious seems second best. Therefore, the buying public, either lacking in sufficient knowledge or appreciation of these stones called semiprecious by their salesmen, or unable to find them for sale by a dealer who has the knowledge and appreciation that they themselves lack, buy synthetics or glass imitations in preference to the doubtful value of a semi-precious thing. Why should we discourage sales by continuing the use of thing term? It should be abandoned totally.

Gold Colors and Mixture

GEM TREATMENTS

Yellow Gold	Gold with Copper and Silver Alloys
White Gold	Gold Nickel, Zinc, silver
Green Gold	Gold with Silver, sometimes Copper and Zinc
Red Gold	Gold with Copper
Pink Gold	Gold with Copper
Today buying an absolutely natural gem is an exception than the rule. Gem treatments are practiced since the antiquity to enhance their overall appearance and nowadays most gems are treated one way or another. A treatment is not always enhancement. For instance, two gems may appear similar, but when they are treated exactly under the same conditions their resultant appearance may be different. Although the gemological properties in most treated gems remain essentially the same, their physical and chemical properties are altered. In treating gems there are many "gray areas" that deserve special attention and consideration.
Examples of Gem Treatments of the Big Four Diamond. Occasionally irradiated and/or heated to produce yellow, green and other fancy colors; the process is not stable. Often, diamonds are laser-drilled to improve clarity/color; the process is stable but controversial. Occasionally coated to improve their color; the process is stable. Often, filling the cracks/cavities with/without colored fluxes to improve clarity; stability is variable. Brownish diamonds may be subjected to HTHP process to produce white colors; the process is reportedly stable and irreversible. Emerald. Commonly treated by inducing colorless or colored oils, resins, oleoresins with or without hardeners from its surface-reaching cracks into the gem's interior to improve clarity/color; the treatment is not stable and special handling/care is required. The process is reversible. Ruby. Commonly heated to reduce purple tinge, blue patches, remove silk and improve color. Commonly filling the surface-reaching fractures and surface cavities/pits with additives to improve clarity and/or color; these heating processes are stable. Blue Sapphire. Commonly heated in various methods with/without additives to improve/develop new color; the treatment is stable. Occasionally, surface color diffusion treatment produce uniform blue color which can be removed after repolishing the stone.
Types of Gem Treatments. Gems are subject to irradiation, thermal, chemical and other types of treatments. Often, several types of different treatments are applied to the same gem as part of the process sought. For instance, in treating near-colorless topaz, certain dose of irradiation is applied first, followed by heating to obtain the final blue color we all see at the jewelry store display counters. The results obtained after the gems are treated varied greatly. This is true in heat-treating ruby-sapphire where the reliability of the equipment and technology used in the process is of paramount importance.
Most important types of treatments applied to gemstones Type of Treatment Examples of Treated Gemstones HEATING: Ruby, Sapphire, Beryl, Tourmaline, Zircon, Quartz FRACTURE FILLING: Ruby, Sapphire, Emerald, Diamond, Tourmaline RADIATION: Diamond, Beryls, Quartz, Topaz, Tourmaline, Pearl DYEING: Jade, Agate, Sodalite NOTE: Only certain types of above listed sample gems are treated and not always Mohs hardness Mineral Chemical formula Absolute hardness Image 1 Talc Mg3Si4O10(OH)2 1 2 Gypsum CaSO4•2H2O 3 3 Calcite CaCO3 9 4 Fluorite CaF2 21 5 Apatite Ca5(PO4)3(OH–,Cl–,F–) 48 6 Orthoclase Feldspar KAlSi3O8 72 7 Quartz SiO2 100 8 Topaz Al2SiO4(OH–,F–)2 200 9 Corundum Al2O3 400 10 Diamond C 1600 The table below incorporates additional substances that may fall between levels: Hardness Substance or mineral 0.2–0.3 caesium, rubidium 0.5–0.6 lithium, sodium, potassium 1 talc 1.5 gallium, strontium, indium, tin, barium, thallium, lead, graphite 2 hexagonal boron nitride,[10] calcium, selenium, cadmium, sulfur, tellurium, bismuth 2.5 to 3 magnesium, gold, silver, aluminium, zinc, lanthanum, cerium, jet (lignite) 3 calcite, copper, arsenic, antimony, thorium, dentin 4 fluorite, iron, nickel 4 to 4.5 platinum, steel 5 apatite, cobalt, zirconium, palladium, tooth enamel, obsidian (volcanic glass) 5.5 beryllium, molybdenum, hafnium 6 orthoclase, titanium, manganese, germanium, niobium, rhodium, uranium 6 to 7 glass, fused quartz, iron pyrite, silicon, ruthenium, iridium, tantalum, opal 7 quartz, vanadium, osmium, rhenium 7.5 to 8 hardened steel, tungsten, emerald, spinel 8 topaz, cubic zirconia 8.5 chrysoberyl, chromium 9-9.5 corundum, silicon carbide (carborundum), tungsten carbide, titanium carbide, stishovite 9.5–10 rhenium diboride, tantalum carbide, titanium diboride, boron [11][12][13] 10 diamond >10 nanocrystalline diamond (hyperdiamond, ultrahard fullerite)

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