Burma Ruby    CORUNDUM     Star Sapphire

Corundum is crystalline aluminum oxide, Al2O3, second hardest on Mohs Scale, and one of the most popular (and expensive) of gem minerals. Ruby is red corundum; all other colors are Sapphire. Sapphire is commonly used to denote blue corundum, with others named according to color, e.g. pink sapphire, yellow sapphire, etc.. The name Star Sapphire is reserved for asteriated, blue corundum. Paradoxically, star stones that are not blue are sometimes referred to as Star Ruby, even those that are not red! Padparadscha (pod-pa-Rah-sha; lotus flower) is an ill-defined name for rare pinkish orange sapphire. The chromophore in ruby is Cr (+ Fe), in blue sapphire Fe and Ti, in yellow sapphire Fe and/or a yellow color center. Padparadscha is colored by trace impurities of Cr and Fe, with or without a yellow color center. Some green sapphire contains trace amounts of Ni as a chromophore. Pure corundum is colorless.

    Corundum is a relatively common mineral that once found wide application as an industrial abrasive. Gem corundum is mined almost exclusively from gem gravel deposits. These deposits are derived from the weathering of high temperature metamorphic (marble, gneiss) or igneous (volcanic or pegmatitic) source terrains. Historically, the most famous and prolific production has been from Myanmar (ne Burma), Thailand, India and Sri Lanka (ne Ceylon). More recent important sources include Australia and the East African countries of Tanzania and Kenya.

    Corundum was the first gem mineral to be synthesized in the lab by a process known today as flame fusion. A somewhat more difficult process, flux growth, is also used to synthesize gem corundum. Synthetic rubies and sapphires are presently manufactured in enormous quantities for both industrial and gem application. Although no longer widely used as an abrasive (silicon carbide [H=9.5] and diamond bort or carbonado are used instead), industrial applications today include use as "jewel" bearings in instruments and fine watches, and as a source of stimulated emission in ruby lasers. Because of its hardness, clarity and ease of synthesis, synthetic corundum is also used today for windows in optical scanning devices, like those in grocery store checkout counters.

    The advent of synthetic corundum in the first decade of this century caused widespread apprehension and greatly diminished ruby sales. Extensive British ruby and sapphire mining operations in southeast Asia, particularly in Burma, suffered greatly from the resulting fall in prices and never recovered. Curtailed mining operations were finally closed after voluntary liquidation in the late 1920's. Though extensive and rich deposits apparently still remain, ruby production today from Myanmar is only a fraction of what it was at the turn of the century.

    As discussed below, the color and clarity of rubies and sapphires is commonly enhanced by heat treatment and, less frequently, by irradiation. Although not commonly disclosed by retailers, such processes are widely acknowledged within the industry and are probably today the rule rather than the exception.  Reliably distinguishing among treated, untreated, natural and synthetic ruby and sapphire depends critically on microscopic examination of inclusions and crystal growth features.

Properties

  • Crystal System: Hexagonal
  • Habit: Usually as well-formed hexagonal prisms with or without rhombohedral terminations. Sapphire often as elongate prisms; ruby usually stubby, flat prisms. Waterworn pebbles are often rounded variants of these shapes.
  • Hardness: 9
  • Cleavage: None; often a basal and rhombohedral parting, however.
  • Toughness: Excellent
  • Specific Gravity: 4.00 (3.99-4.02)
  • R.I.: Intermediate; 1.761-1.769 (reported range 1.757-1.778)
  • Birefringence: Low (0.008-0.009)
  • Dispersion: Low (0.018)
  • Pleochroism: strong, with deepest color perpendicular to c axis:
    • Ruby - intense purple-red to lighter orange-red
    • Blue Sapphire - violet-blue to lighter greenish-blue
    • Orange Sapphire - orange to lighter yellow brown or pale orange
    • Purple Sapphire - violet to orange
    • Yellow Sapphire - yellow to pale yellow
    • Green Sapphire - green to blue-green and yellow-green.
    • Pink Sapphire - hot pink to pale pink or more red.
  • Asterism: 6 (more rarely 12)-rayed star due to oriented rutile needles.
  • U.V. Fluorescence: varies with place of origin (Fe content);
    • Burmese Ruby - strong red (Cr); best stones fluoresce in strong sunlight.
    • Thai Ruby - less intense red (Cr+Fe); may show patchy blue fluorescence if heat treated.
    • Sri Lankan Ruby - strong orange red in long u.v.,less strong in short u.v. (Cr).
    • Pink Sapphire - same as above.
    • Padparadscha - same as above. Heat treated may show strong reddish orange in short and long u.v..
    • Green and most yellow Sapphire - none (Fe + Ni + Ti).
    • Blue Sapphire - none (most; Fe + Ti) to red or orange (Kashmir, Sri Lanka, Montana) in long wavelength u.v.. Heat treated stones may show a dull chalky green fluorescence in short u.v..
    • Colorless - moderate light red to orange

Distinguishing Properties

RUBY

  • Distinguished from red spinel, garnet or glass (all isotropic) with polariscope.  R.I. for other red stones is sufficiently different to distinguish.
  • From synthetic ruby by microscopic examination or fluorescence in a few cases.
    • Synthetic ruby grown by the flame fusion technique usually shows curved growth striations or curved color zoning, and may contain unmelted grains and gas bubbles. Growth stria and color zoning are best observed by examining stones through the table because of the way synthetics are oriented for cutting; the c-axis, which is parallel to the long dimension of the boule in flame fusion corundum, lies parallel to the table of gem stones cut from these boules, whereas natural ruby is often cut with the c-axis perpendicular to the table.
    • Under short wave u.v., flame fusion synthetic rubies often show a brighter red fluorescence than naturals, though the test is nondiagnostic because some Cr-rich synthetic varieties are less fluorescent, and the best Burmese gems are as fluorescent as most synthetics.
    • Flux growth synthetic rubies (e.g. Ramaura ruby) may contain flux inclusions (orange or white in color if PbO or PbF flux is used).
    • Flux-growth Ramaura ruby in our collection fluoresces a strong red in long wavelength u.v. light but shows little to no fluorescence in short wave u.v.. Some Ramaura ruby apparently also fluoresces strongly in short wavelength u.v.  Fluorescence in both short and long u.v. is said to be more yellow-orange than that observed in natural ruby.
    • In all cases, synthetic ruby lacks the natural mineral or fluid inclusions that are distinctive for ruby from all sources (see below).

SAPPHIRE

  • From blue or other spinel by polariscope and R.I., from others by high S.G. and R.I..
  • From synthetic sapphire by inclusions and by same features listed above. Curved striations and color zoning in flame fusion synthetics are less visible than in synthetic ruby, but can sometimes be seen if the gem is placed in immersion liquid.
    • Under short wavelength u.v. light, synthetic blue sapphires show a bluish-white or greenish glow, which is only very rarely encountered in natural sapphire.
    • Synthetic purple or violet sapphire resembling amethyst in color glows bluish-white in short wavelength u.v. light and red in long wavelength u.v..
    • Natural yellow sapphire will sometimes fluoresce in short u.v. light; synthetic yellows will not.
    • Synthetic "Alexandrite-like" color-change sapphire in which Vanadium is added will show prominent growth lines and a characteristic purple-mauve color.

Ruby

    The king of gems. In sizes over 10 carats, Burmese stones of the highest quality are, per carat, the most costly of all gems. Birthstone for July. Color is of principle importance in pricing. "Burma" rubies are renowned for an intense, medium, pure to slightly purplish red color, whether from Burma or not. The ill-defined adjective "pigeon blood" has been used to describe this color, though its precise meaning today is so obscure that the term is virtually meaningless. The best, true Burma rubies show a red, warm glow in direct sunlight, a consequence of strong u.v. fluorescence peculiar to these stones that are colored by Cr without any Fe present.  "Thai" or "Siam" rubies are commonly darker, with a darker tone and weaker saturation (Fe present), and comprise most of the stones on the market today.  Some or all of these darker overtones are today commonly removed by heat treatment.  "Ceylon" ruby was once a common term for light red to pinkish ruby that in most cases could more properly be referred to as pink sapphire.  It should be emphasized these names today have very little to no meaning with regard to a rubies origin (they probably never did, given the inconsistencies of their use and the broad range of colors produced at all localities) because of the now widespread use of color enhancement techniques (see below).

    The term "Balas Ruby" is an old misnomer that was once used for red spinel, and is not ruby at all.

    Prior to the mid 1960's, much of the ruby sold in America originated from Burma. Discerning jewels and gemologists considered Thai rubies to be greatly inferior to the lighter, purer red, Burma varieties; these stones were consequently worth considerably less. Production in Burma nearly ceased after socialists seized power in 1962, and today accounts for an extremely small portion of fine rubies that annually make it to market. Thai rubies have since become the norm (average consumers describe ruby as "dark red") and have experienced a tremendous price increase. The lighter, purer-red, Burmese varieties are still the most highly prized, but are rarely seen in jewelry stores today. The common notion that the best rubies are very dark red must be dispelled when purchasing fine gem ruby.

Sources

  • A. Myanmar (ne Burma) - Worlds finest rubies from Mogok Stone Tract; since at least 1597 A.D. (historical records); perhaps as far back as the Neolithic (stone tools found in the area).  Recent production (beginning ca. 1992) from a new locality, Mong Hsu, belies the superlative "Burma Ruby" moniker.  These are not nearly the quality of Mogok ruby, commonly requiring  heating and filling to yield viable gems.  By far the most definitive work on Burma corundum is that by Hughes, which is now online and makes fascinating reading.   Mogok ruby has the following characteristics:
    • Originate in marble formed by contact(?) or regional(?) metamorphism of impure limestone. Mines are in gem gravel deposits.
    • Inclusions of rutile, calcite, apatite, olivine, sphene, spinel.
    • Give off a strong red fluorescence in short and long u.v. light.
    • Most prolific production during the period 1889-1931, when the area was mined on a large scale by Burma Ruby Mines Ltd., a British concern run by an eminent London jeweler, Edwin Streeter.
    • Mining on a small scale by native miners using primitive methods from 1931-1963, except during W.W.II.
    • Private gem mining officially ceased by the socialist governments decree in 1962; mines nationalized in 1963. Mining continues today through government leases to Myanmar nationals.  Some production is sold at government-sponsored auctions in Rangoon, some changes hand privately via smuggling through Thailand.
  • B. Thailand - once about 70% of world production. Important because of lack of commercial mining in Burma.
    • Darker red; brownish to purplish overtone due to Fe
    • 85-90% from the Chanthaburi-Trat gem field (since 1850?), 330 km SE of Bangkok.
    • Mining restricted to Thai nationals since 1919.
    • In lateritic soils atop Plio-Pliestocene basalt, or in gem gravels derived from basalt. Deposits are about 6-20' below the surface.
    • Source is thought to be basalt (corundum xenocrystic?).
    • More Fe-rich than Burma ruby, show a much weaker red than Burmese stones in short and long u.v..
    • Characteristic inclusion is pyrrhotite (iron sulfide).
  •  C. Sri Lanka - most of the rest of the worlds production (since 200 A.D.?).
    • Main deposits (gem gravels) in the Ratnapura district, about 100 km S.E. of Colombo, and Elahera district (115 km NE of Colombo).
    • Rubies are typically more pinkish (could be referred to as pink sapphire in some cases) than those of Burma or Thailand.
    • Characterized by sparse, long, rutile inclusions, and included zircons with radiation halos.
    • Give off a strong orange-red in long u.v. light.
    • Deposits have yielded some exceptional star stones (e.g. Rosser Reeves in Smithsonian).
  • D. Cambodia - Pailin Gem Fields
    • Cross-border extension of the Thai gem fields; same characteristics as Thai ruby.
  • E. Others - Vietnam, East Africa (Kenya, Tanzania; exceptional color, generally fair to poor clarity for material produced prior to 1984, new finds are said to rival Burmese for color and clarity, after heating), Australia (mostly sapphire), India (mostly lower quality stars and cab. material), Madagascar, Pakistan, Afghanistan, Nepal.

Shaping and Treatment

  • Step or brilliant cut; heavily flawed or star stones are cut en cabochon.
  • Much ruby rough is shallow; many cut stones are shallow as a consequence. Because of strong dichroism, the best color is attained by cutting the table normal to the c-axis. Ruby cut this way will look dark in all orientations when placed table-down on a polariscope. Stones cut for weight in any other orientation tend to show more orange in the color than those cut with the table normal to c.
  • Heating is used to remove dark brownish or purplish overtones in "Thai" and other rubies and lighten the color. According to most reports, this is a now common practice. Faceted stones that have undergone such a treatment have to be repolished; double girdles, pock-marks, or other indication of repolishing sometimes a clue to treatment. CO2 inclusions will not survive high temperature treatment; their presence is good indication of no heat treatment. Discoid fracture patterns around natural mineral inclusions are also a sign of heating.
  • Asterism can be induced in stones containing sufficient Ti by heating for an extended period at about 1300oC (rutile needles form). Can also be eliminated by heating to higher temperature (1600-1900oC) for short period (rutile dissolves).
  • A surface diffusion process is also used to enhance color in weakly colored material. Can be detected by color concentration along facet junctions, in surface-reaching fractures and around the girdle.
  • Clarity is now commonly enhanced by "flux-healing", particularly in Mong Hsu ruby.  See Hughes for an excellent description of this process.  Standardized laboratory grading terminology now includes terms to describe the extent of such treatment.

Pricing and Valuation

  • Priced on a per carat basis, according to color, clarity and size of stone.
  • An excellent discussion of the factors involved in judging quality can be found in Chapter 10 of Hughes.  A table of famous rubies can also be found there.
  • Finest quality, in 10 carat or larger sizes have sold at auction for over $100,000/carat!  ($3,630,000 was paid for a 15.97 ct Burmese ruby in 1988; that's more than $225,000/ct!).  $1,239,000 was paid in 2000 for a 9.98 ct Burmese ruby set in ring with diamonds.
  • Finest quality in the 1-2 carat range was selling for about $6,000/carat (wholesale) in 1990.  Price trends (retail) for the same material over a 25 year period show a recent increase.
  • Commercial grade ("Thai" or Mong Hsu; poorer color, +inclusions, poor cut) stones of the same size was selling for about $100-1000/ct (wholesale) in 1990, as it is today.
  • Fine gemstones of documented Burmese (Mogok only) origin sell for a premium. A 3 carat unheated Mogok ruby can sell for as much as 3 times the price of a treated Thai or Burma counterpart. The price difference decreases in smaller stones (50% premium for 1 carat stones; 25% premium for melee).
  • Proper cut and proportions important, as in all stones. Beware of shallow cuts.
  • Ruby made by flame fusion or crystal pulling techniques is manufactured in enormous quantities and sells for a few dollars a carat. Flux-grown synthetic rubies manufactured by J.O. Crystal Company ("Ramaura Ruby"), Chatham, and others are considerably more expensive. They are sold in 4, inclusion-based, grades (Gem, Fine, A, B) and several size (weight) categories. Sub-carat, Gem grade stones sold for about $200/carat and 5-6 carat Gem grade stones for $350/carat in 1989 (wholesale). Grade A stones are 1/3 to 1/2 of these prices. The flux-growth process typically yields quite thin ruby crystals; as a result, a lot of the stones being offered are quite shallowly cut. Other manufactures of flux-growth rubies include Gilson, Kashan (now defunct), Knischka, and Lechleitner.
  • Despite disingenuous claims to the contrary, the flux growth process does not more closely resemble natural ruby growth processes (i.e. solid-state metamorphic processes; gem ruby and sapphire do not crystallize from magma even though they do occur in volcanic rocks) than synthesis by flame fusion or crystal pulling.  As for looking "more natural", once faceted all types of synthetic ruby are, to the naked eye, indistinguishable (see this for yourself in lab) and both so closely resemble fine natural ruby that only very careful, microscopic examination reveals a difference.  Why do people pay two orders of magnitude more for flux-growth synthetic ruby when much less expensive, essentially identical flame fusion ruby is available?  Advertising, lack of knowledge, and "price guilt" are prime factors; there appear to be no gemological/mineralogical reasons to do so.
  • Star Ruby
        Fine red star rubies are one of the most expensive of all colored stones. Fine gemstones are exceeding rare, more so now because of the recent, widespread(?) practice of heating potential star rough to turn it into clear ruby. At its best, star ruby has the body color of Burma ruby (no brown, little to no purple). As in all fine star stones, the star should be centered, with sharp (not wide or blurry) rays that extend to the base of the cab. The star itself should be silvery or milky white with no "bleed-through" of red. Top stones are translucent. Prices per carat for the best gems can those of the best Burmese ruby.
        Asterism can be (and is) induced in some ruby by a surface diffusion process. TiO2 powder is painted on a ruby cab., which is then heated to near melting temperatures. TiO2 diffuses into outer few microns of the stone. Cooling and subsequent annealing produces aligned rutile needles in a thin outer layer, resulting in a star.

Sapphire

    Birthstone for September. Occurs in a wide range of colors (blue, pink, "padparadscha", orange, yellow, green, purple, black, colorless). Color is due to trace impurities of Fe2+, Fe3+ and Ti, and/or a yellow color center. The most desirable (i.e. expensive) color is an intense "cornflower" blue; these are sometimes referred to as "Kashmir" sapphires. At their best these have a very saturated, slightly milky, violet blue color. Padparadscha (see above) is next in value, followed by pink, then orange, purple and yellow, respectively. Though sometimes touted as a good investment, green sapphires are not currently, and have not historically been, of great value. The color of most sapphire can be altered through heat treatment (see below) and/or irradiation.

Sources

  • - Major producers same as ruby (Burma, Thailand, Sri Lanka), plus Australia and East Africa (Tanzania, Kenya, Nigeria, with lesser amounts from Malawi and Burimundi).  Production in Thailand has seen a dramatic decrease in recent years.  All mined in gem gravels or clay resting on basalt. Some of the finest blue sapphire currently being mined comes from the Rakwana district of Sri Lanka.

    - Sources of note:

    • 1) Kashmir, India; discovered 1881. Deposit in a remote Himalayan glacial valley where corundum occurs in association with pegmatite veins in marble. Found in pockets where plagioclase altered to clay; could be scooped out by hand. Mines were thought to be essential depleted(?) by 1925, when mining was greatly curtailed. Later mineral survey revealed much of the valley floor is underlain by sapphire-rich soil. Has been no official sales of Kashmir rough for 20 years. Mines not currently active, though locals are said to mine clandestinely. True Kashmir sapphire rare.
      • Color is described as an "unrivalled" blue; a quintessential rich, royal, velvety blue with a fine satiny luster.
      • All shows color zoning; diagnostic
      • Proving a Kashmir origin is difficult at best, impossible in most cases without papers that document source of origin and history of stone.
      • May contain inclusions of green mica, tourmaline, and/or fine rutile.
    • 2) Burma - Mogok stone tract.  Considered second only to Kashmir sapphire.
      • Believed to have originated in pegmatites and nepheline-corundum syenites (not in the marbles that contain ruby); mined from gem gravels.
      • Color is exceptionally even; commonly lacks color banding typical of Sri Lankan blue sapphire, which it otherwise closely resembles.  Rich   "intense" blues, verging on violet are considered the best, but lighter blues are more common. Purple, straw yellow and green are also found.
    • 3) Montana (Missouri River, NE of Helena, also Yogo Gulch, near Utica); discovered 1865, 1895. Also from Rock Creek in Granite Co.. Early and continued sources of much industrial-grade material. Also the source of considerable gem material (about $25 million from Yogo Gulch from 1895-1929).
      Gold and sapphires in Missouri river gravels mined intermittently from 1865-present. Sapphires usually quite small, well-rounded or flat, and of a pale blue or blue-green color.
      • Best Yogo Gulch blue sapphire are said to rival Kashmir for color, show better clarity. Majority are a paler blue or have a greenish tint. Some are a lovely purplish-blue. Color most commonly associated with the term "Montana Sapphire" is stone of medium to light tone, very transparent, with what has been described as a steely gray blue or somewhat metallic blue color.
      • Rough is typically small (most yield subcarat stones), often shallow. Rough that will produce a gemstone of 2 carats or more is rare.
      • Yogo Gulch mine is in 2-8' wide dike that cuts limestone. Hard rock mining techniques and American labor makes mining relatively expensive, less economic than East Asian counterparts.
      • Yogo Gulch first mined on a large scale by an English sapphire syndicate, beginning in 1898. Production nearly halted during W.W.I. Following war, worker and water shortages, production problems, and double taxation (British and U.S.) led to closing in 1929. Mine reopened in 1956. Since then no less than 13 attempts have been made to reestablish Yogo sapphire production. All produced sapphire, none did so economically. Current (1993) owner and operator is Rancor Inc. (since 1985?) and Vortex mining who are developing a recently discovered extension of the dike. Geological surveys indicate a minimum of 28 million carats are still in the ground, making this one of the largest proven deposits in the world.
    • 4) Australia (Queensland: Anakie and Lava Plains districts; New South Wales: Glenn Innes and Inverell districts); discovered 1870, 1960 respectively.
      • Gem dirt (alluvium) at the surface, to 50 ft. thick atop weathered basalt.
      • Anakie noted for fine yellows, also some very fine blue but most has been characterized as "inky" (too dark) or strongly dichroic dark blue and green; some production of pink and orange as well.
      • Dark sapphires are bought by Thai dealers and others who lighten the color by heat treatment (see below).
      • Currently a major producer (50-70% of world production in 1990, according to one source).
    • 5) Tanzania; Umba River Valley near Kenyan border; since 1962.
      • sapphire in a "corundum pipe" (dike?, basalt flow?)4 miles in diameter.
      • according to one source, the market in "East African" corundum was cornered in 1965 by a group of dealers; most rough still uncut.
      • noted for past production of fine orange-pink (some consider the brown overtone present in these stones precludes the padparadscha moniker), deep purples, dark, untreated golden yellows, and color-change (i.e. alexandrite-like) sapphires.
      • Also specimen and some gem grade ruby in green zoisite rock (a.k.a Ruby in Chrome Zoisite) at Longido
    • 6) Others: Pakistan, Cambodia (Pailin Gem Fields), Malawi, Colombia, Brazil, Nigeria, China, Zimbabwe, Madagascar.

    Shaping and Treatment

    • Faceted in both step and brilliant cuts. Star stones and included rough cut en cabochon. - Heat treatment of sapphire is a widespread practice (nearly ubiquitous?), irradiation less so. Following treatments and results have been noted:
      • Heating in open crucible from 1500-1900oC of pale yellow or nearly colorless stone can yield a rich dark yellow, golden, golden-brown, orange, or reddish-brown color (Fe2+ oxidized to Fe3+). Pink with some Cr can be heated to give stable padparadscha orange-pink color.
      • Very dark blue can be lightened by a few minutes at 1200oC in an open, nonreducing vessel (Fe2+ oxidized to Fe3+).
      • Whitish or pale blue containing masses of fine rutile ("silk"), called Geuda by Sri Lankans, can be heated in air to 1200oC to remove blue; heating to around 1900oC will restore blue and remove silk.
      • Irradiation can convert some pinks to padparadscha. Heating of irradiated stones will restore the original color (yellow color center destroyed).
    • A "surface diffusion" method of treatment can be used to darken the color of pale blue sapphire, or turn white sapphire blue. Method involves coating stone with TiO2 and Fe-oxide powder and heating to near melting temperatures. Ti and Fe diffuse into outer few microns of stone, yielding a very thin, skin-like layer of blue color. Immersion in oil will reveal this (see strong color zoning, darker color ring around the girdle and along facet junctions), as will bleeding of color around cracks and pits.
    • A more recent, controversial variant, involving "bulk diffusion", relies upon the diffusion of beryllium and/or other light elements at very high temperatures into natural colorless or pink sapphires, yielding yellow, yellow-orange and orange sapphire, and padparadscha.  Purplish red rubies treated by the same technique may become a purer red.
    • There are means to detect most heat treatments that include examination of inclusions, dichroism, and fluorescence.  Simple techniques for detecting diffusion treatments rely on detection of color zoning of unnatural appearance, or of microscopic recrystallized overgrowths (also termed "re-deposition").  Unfortunately, bulk diffusion that involves beryllium can yield stones with no discernable color zoning or overgrowths, requiring much more sophisticated laboratory testing.

    Pricing and Valuation

    • As per ruby. Darker blue stones that most jewelers carry are not as valuable as lighter-toned, bright, intense blue material.  Darker stones have become the commercial standard; most consumers would not recognize a Kashmir or Burma blue as the extremely fine gems that they are.
    • An excellent discussion of evaluating quality in sapphire can be found in Chapter 10 of Hughes (1997).  A table of famous sapphires can be found there also.
    • Finest quality 1-2 carat stones were in the following wholesale ranges in 1990:
      • Blue - $1,000-5,000/carat
      • Padparadscha - $1000-2000/carat
      • "Hot" Pink - $500-800/carat
      • Orange - $300-600/carat
      • Golden - $200-400/carat
      • Purple - $200-500/carat
      • Yellow - $50-100/carat
      • Green - $50-80/carat
    • More recent sources of wholesale prices for the finest blue and pink sapphire are similar, with perhaps a slight increases for pink sapphire.
    • Prices for 1 to 2 carat, commercial grade blues and pinks are about 1/10th or less of the above prices.
    • Blue stones are best with a violet overtone; a green overtone is less desirable, as are gray-tinged or lightly colored blues.
    • Large (15-35 ct) Kashmir sapphire have recently (2000) sold at auction for $19,500 to $24,300 per carat.
  • Pinks should be of uniform color. Best is "hot" pink; little to no lavender or brown overtone.
  • Purple should resemble fine amethyst, but somewhat redder.
  • Stay away from yellows with a brownish cast. Golden yellows or orangish yellows are worth more than pure yellows, but the former may be produced in large amounts with heat treatment and the latter by diffusion/heating, so this generalization may no longer apply.
  • Greens should not show an olive or gray tinge, and should be free of mottling or strong color zoning.
  • Synthetic blue sapphire and "padparadscha" are made by Chatham and several others. Sold in grades, as per ruby. Chatham Gem Grade, 1989 wholesale to 1.5 carats costs $215/carat; at 10 carats $540/carat. Grade A stones sell for 1/2-1/3 as much in comparable sizes. These synthetics are manufactured by a flux growth technique; sapphire made by flame fusion (Verneuil process) are considerably less (pennies/carat).

Star Sapphire

    Star sapphire is the result of reflection of light from fine, oriented, rutile needles. Like star ruby, star sapphires may be heat treated to high temperatures to dissolve the rutile and produce blue sapphires of good clarity. Such has been the recent fate of much of the Sri Lankan Geuda material that might have otherwise been uncutable (too dark and/or cloudy). Unfortunately, some reports state that much of the good star material is now suffering the same fate. The same characteristics apply to good star sapphire as to star ruby (see above). The best body color is an intense pure blue, but such natural stones are rare and one more frequently encounters blues that are more gray. Fine blues are more translucent than even good gray-blues and are cabbed thicker as a result. Such stones may appear to be "overweight" with bulky bases, an important consideration when paying by weight but a necessity to maintain a deep blue color. This is not the case for average blue stones, however, and you should not pay for excess weight unnecessarily.

    Synthetic star sapphire (and ruby) was first made by Union Carbide ("Linde Stars") in the late 1940's. These synthetics, and those currently being made by Nakazumi Earth Crystals in Japan, are superior in the straightness and narrowness of the star and the outstanding deep blue body color. These characteristics are sufficient to distinguish these synthetics from all but a handful of naturals; one author states that the stars look so vivid and intense that they appear to be painted on the stone rather than emanating from within it. These do not have to be cut as deep to maintain color, and this can serve as a tip off as well.

Prices

  • Finest quality blue star sapphire in the 5 carat range was selling for about $2500-3000/ct (wholesale) in 1990.
  • Commercial grade stones (whitish or grayish blue, poorer star) of similar weight sold for $50-300/ct.
  • Black star sapphire of even the finest quality generally sell for under $50/ct (wholesale), ranging down to $1-2/ct for commercial quality stones of small size.

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1998
Updated 08/24/12
Comments and questions to helper@mail.utexas.edu
Department of Geological Sciences
The University of Texas at Austin