Sapphire

saf-ahyuh r
September Birthstone

September's birthstone has come a long way since the days when any and every blue stone was called a sapphire. Though its fame is shared with its "Big Three" counterparts ruby and emerald, sapphire has enjoyed a long run as one of the world's most beloved gemstones, earning itself a place of honor in crown jewels, royal accessories, museums, and even in modern royal engagement rings. Lest sapphire get too haughty, it has common uses as well. The rough polishing material on emery boards is made up of lower-quality corundum grains, strengthened with hematite, magnetite and quartz.

Sapphire Polished
Sapphire Classification
Common Name Sapphire
Species Corundum
Sapphire Optical Properties
Transparency Transparent - Opaque
Dispersion Strength: Moderate Fire Value: 0.018
Refractive Index 1.762-1.770
Tolerance:(+0.009/-0.005)
Birefringence 0.008-0.01
Optic Character Uniaxial
Optic Sign Negative
Polariscope Reaction Doubly Refractive (DR)
Fluorescence SWUV: Inert to weak chalky blue or yellowish green
LWUV: Inert to weak red to orange
Pleochroism Dichroic, moderate to strong, varying shades of body color
Sapphire Characteristic Physical Properties
Hardness 9
Streak White
Specific Gravity 3.950-4.100 Range:0.1/-0.05 Typical:4.000
Toughness Good
Inclusions Sapphire has type II clarity. Sometimes have silk, rutile, boehmite, apatite, calcite or zircon crystals. Fingerprint and negative crystal inclusions. Hexagonal growth and color zoning. Untreated stones will usually have inclusions intact. Heat treated stones will have fracture halos, discoid fractures or snowballs around crystal inclusions (untreated stones from magmatic areas might also show these characteristics). Silk will be broken and might show sintered areas especially around the girdle.
Luster Bright Vitreous
Stability Very Good
Fracture Conchoidal
Cleavage None
Sapphire Chemistry & Crystallography
Chemical Name aluminum oxide
Chemical Formula Al2O3
Crystal System Trigonal
Chemistry Classification Oxide

Sapphire Colors

  • Bi-color Sapphire Bi-color
  • White Sapphire White
  • Red Sapphire Red
  • Multi-color Sapphire Multi-color
  • Green Sapphire Green
  • Gray Sapphire Gray
  • Colorless Sapphire Colorless
  • Brown Sapphire Brown
  • Black Sapphire Black

Sapphire Spectra

Sapphire Spectra
Sapphire

Color due to chromium. Fluorescing emission doublet in the red at 693/694nm. And general absorption in the yellow green. There is no evidence of any lines in the blue.

Sapphire Spectra
SAPPHIRE. - Verneuil Lab Created (Unpolarized.)

Color due to chromium. Broad absorption in the yellow and most of the green. A very faint emission line at 693/694nm. Dark lines in the blue at 468nm. and 476nm.

Sapphire Spectra
SAPPHIRE. - Verneuil Lab Created (ω ray)

Color due to chromium. Using a polarizing filter to isolate the ordinary ray strengthens the absorption band in the green. Broad strong absorption in the yellow and most of the green. A strong emission line at 693/694nm. Very faint lines detected in the blue at 468nm. and 476nm

Sapphire Spectra
SAPPHIRE. - Verneuil Lab Created (ε ray)

Color due to chromium. Weak broad absorption in the yellow and most of the green. A very faint emission doublet in the red. No lines are seen in the blue, making it difficult to ID.

Sapphire Spectra
Lab created ORANGE SAPPHIRE. (unpolarized

Color due to chromium The initial appearance of body color and spectrum are not unlike those of fire opal However careful observation in the deep red usually reveals the fluorescing doublet at 693/694nm. indicating the presence of chromium. Green is partially absorbed and the remainder totally

Sapphire Spectra
Lab Created ORANGE SAPPHIRE. (fluorescence spectrum in scattered light)

By allowing the minimum of scattered internal specular reflections from a brightly lit gemstone to enter the spectroscope, only the brighter parts in the long wave area are visible as a fluorescence spectrum. Here the dominant doublet is resolved as two lines at 693 and 694nm. The two lines at 659nm. and 668nm. are also captured in fluorescent mode

Sapphire Spectra
Lab Created ORANGE SAPPHIRE. ( ω ray)

Color due to chromium. The initial appearance of body color and spectrum are not unlike those of fire opal However careful observation in the deep red usually reveals the fluorescing doublet at 693/694nm. indicating the presence of chromium. Green is partially absorbed and the remainder totally. Using a polarizing filter to isolate the o- ray will enhance the fluorescence of the doublet in the deep red and confirm the evidence. Now the broad absorption band in the green has strengthened and transmission below 580nm. is weak in accordance with the o-ray.

Sapphire Spectra
Lab Created ORANGE SAPPHIRE. (ε ray

Color due to chromium. The initial appearance of body color and spectrum are not unlike those of fire opal However careful observation in the deep red usually reveals the fluorescing doublet at 693/694nm. indicating the presence of chromium. Green is partially absorbed and the remainder totally. In the e ray the absorption band in the green is much weaker and so is the fluorescence of the doublet in the red .

Sapphire Spectra
SRI-LANKAN SAPPHIRE. (ω ray)

Color mainly due to iron and chromium. The low iron content together with the presence of a little chromium is usually associated with Sri-Lankan yellow sapphires and results in an almost continuous spectrum. A very faint line at 450nm. may be detected if the o-ray is polarized as it is in this direction that is seen to strengthen if present.

Sapphire Spectra
SAPPHIRE.

Color due to iron. As the iron content increases three lines in the blue are seen. As they strengthen and widen the line at 450nm. has merged with the one at 460nm. while the one at 470nm. can just be separated.

Sapphire Spectra
SAPPHIRE

Color due to iron. Wide absorption band seen where all three lines in the blue, typically 450nm, 460nm and 470nm. have merged to form a solid block between 440nm. and 475nm

Sapphire Spectra
SAPPHIRE Verneuil synthetic (Unpolarized)

Color due to vanadium. Chromium may also be present. This spectrum is from the color change corundum marketed as a simulant to alexandrite. In daylight. It is distinguishable by its lavender blue color which changes to a bright purplish red in tungsten light. The mechanism for this change in color can be seen in the spectrum where the broad absorption band centered at 570nm. controls the balance between blue and red. Short wave transmission here starts at about 465 nm. and alongside this at 475nm. can be seen the sharp narrow line diagnostic for this material.

Sapphire Spectra
SAPPHIRE Verneuil synthetic (ω ray)

Dichroism in this color change sapphire is strong and when the o-ray is isolated using a polarizing filter this is evident in the color of the stone and the spectrum. In daylight the stone is more blue and the broad absorption band in the center of the spectrum widens and shifts more towards the long wave side.

Sapphire Spectra
SAPPHIRE Verneuil synthetic (In scattered tungsten light)

When a strong narrow beam is scattered from within the stone fluorescence is activated when chromium is present. We now have the bright chromium fluorescing doublet at 693/694nm. in the deep red.

Sapphire Spectra
SAPPHIRE Verneuil synthetic (Ɛ ray)

Rotating the polarizing filer through 90º will locate the e-ray and the stone becomes more green in daylight. The spectrum reacts accordingly, and the center absorption band becomes narrower and weaker, shifting back to the short wave side centering about 560nm. There is also a little more transmission on the short-wave side of the line at 475nm.

Sapphire Spectra
SAPPHIRE - Verneuil Synthetic blue

Color due to iron. This spectrum, from a deeply colored synthetic blue sapphire, transmits little light and shows no evidence of any lines in the blue around 450nm., which would be expected in a natural sapphire of this color. The broad absorption from 550nm to 600nm., with very little transmission after 620nm., illustrates the saturation of color in this stone.

Sapphire Spectra
SAPPHIRE. (Unpolarized)

Colour due to chromium and iorn.In corundum this hue is difficult to describe it neither red, pink or purple. Based on the chromium and iron balance, some may regard it as an intense deep Padparadscha color. The spectrum at first inspection shows little apart from a faint absorption in the yellow - green and a strong but obscure line in the deep blue at 450nm. as we find in blue sapphire due to iron. The absorption in the red beyond 675nm. obscures any indication of absorption lines in this area

Sapphire Spectra
SAPPHIRE (Scattered light)

Color due to chromium and iron. In corundum this hue is difficult to describe it neither red, pink or purple. Based on the chromium and iron balance, some may regard it as an intense deep Padparadscha color. Adjusting the positions of both stone and light source can suddenly indicate the presence of chromium by revealing the strongly fluorescing doublet in the red at 693/694nm. which is seen here along with the iron line at 450nm. and the absorption in the green. This gives an indication of the balance between these two transition elements in this particular gem corundum.

Sapphire Spectra
SAPPHIRE (ω ray)

Color due to chromium and iron. In corundum this hue is difficult to describe it neither red, pink or purple. Based on the chromium and iron balance, some may regard it as an intense deep Padparadscha color. Using a polarizing filter, the o ray is seen to widen and strengthen the absorption band further into the green and the line at 450nm. is stronger. The absorption in the red beyond 675nm. obscures any indication of absorption lines in this area

Sapphire Spectra
SAPPHIRE (In scattered tungsten light)

Using light scattering technique reveals the full extent of the fluorescence. The main doublet at 693/694nm. is much stronger than would normally be seen and the two other weaker fluorescence lines can be seen at 659nm. and 668nm. Absorption is considerably diminished.

Sapphire Spectra
SAPPHIRE Blue

By using tungsten light, scattered internal reflections in a pale blue sapphire can produce a bright fluorescent line in the deep red indicating the chromium doublet at 693/694nm.

Sapphire Spectra
SAPPHIRE Glass fracture filled

Color mainly due to cobalt in the glass filling. Here a very faint indication of the line 450nm. can be seen but on close inspection other features come to view. The broad absorption band in the yellow would not be so intense in this medium blue sapphire and is due to the additional cobalt band at 590nm. Also the band in the red at 655nm.would not normally be present. The positions of these two bands, which are due to cobalt in the glass fracture, are similar to those in other cobalt glass spectra except here, the one in the green is extremely faint and difficult to resolve.

Sapphire Spectra
SAPPHIRE Flux grown synthetic

Color due to iron. When the scattered internal reflection from the tungsten light enters the spectroscope a weak fluorescence line can be detected in the deep red about 693nm. indicating the possible prescience of chromium.

Sapphire Spectra
SAPPHIRE Flux grown synthetic

Color due to iron. Very little is seen in this Chatham synthetic sapphire spectrum, with an almost continuous spectrum apart from a weak absorption in the yellow and at the extreme long and short wave ends. There is no evidence of the line at 450nm. usually detected in natural blue sapphire.

Sapphire Spectra
SAPPHIRE (ε ray)

Color due to chromium and iron. In corundum this hue is difficult to describe it neither red, pink or purple. Based on the chromium and iron balance, some may regard it as an intense deep Padparadscha color. In the lighter colored e – ray, absorption in the green has almost gone and more transmission beyond the line at 450nm.on the short wave side makes it easier to see. The absorption in the red beyond 675nm. obscures any indication of absorption lines in this area.

Sapphire Spectra
SAPPHIRE (Diffused Color)

Color due to chemical diffusion. The diffusion process is often attributed to addition of iron and titanium. A narrow faint line is seen at 450nm. and a broad band centered at 570nm. These and the strong absorption beyond 650nm. are due to the transfer charge between the two elements. Cobalt has also been used and evidence of this can be seen here with faint bands present at 550nm., 590n.and 630nm. Seen through a Chelsea filter the stone appears a weak purplish red.

Sapphire Spectra
SAPPHIRE Composite

Color from synthetic sapphire pavilion. The blue synthetic sapphire pavilion in this stone is the cause of the broad absorption from 550nm to 600nm., with very little transmission after 620nm. There is a single line at 450nm. in the deep blue. This is due to the natural green sapphire which forms the crown part of this composite stone and would be expected to be absent in a purely synthetic sapphire.

Sapphire Spectra
SAPPHIRE

Color due to iron. In the spectrum of this dark brown stone, we have a strong band in the deep blue centered at 460nm. On close inspection this band is seen to consist of three strong lines at 450/460/470nm. merged as one broad band which is indicative of sapphire with a very high iron content.

Sapphire Spectra
SAPPHIRE - Natural Color Change

Color due to iron and chromium. Observing the spectrum of this natural color change sapphire, the central absorption band is placed strategically to trigger a color shift according to the energy source. The iron content here is very low with no sign of the usual absorption features in the blue area. Here there are however faint indications of the lines due to chromium at 468nm. and 475/476nm. and with scrutiny a faint fluorescence line can be detected at 693/694nm. in the deep red.

Sapphire Spectra
SAPPHIRE Blue

Color due to iron-titanium transfer charge and Fe3+-Fe3+ With increase in ferric iron content the color of sapphire darkens and the band at 450nm is stronger and merges with another at 460nm; with a weaker one appearing at 471nm. Absorption in the yellow and red areas is strong due to the iron-titanium transfer charge. This is typical of many dark untreated Australian sapphires.

Sapphire Spectra
SAPPHIRE Blue

Color due to chromium and iron. Pale blue Sri-Lankan sapphire seldom shows any evidence of absorption lines in the blue with almost a continuous spectrum apart from a weak absorption in the yellow. However chromium is often present and this can be detected by viewing the spectrum in scattered tungsten light.

Sapphire Spectra
SAPPHIRE - Blue

Color mainly due to Fe2+-Ti4+ This spectrum os from a fine blue untreated sapphire and shows that the red is absorbed down to about 620nm. and there is broad absorption centered at 580nm. This is due to the iron - titanium transfer charge and the cause of the fine blue color. A weak narrow line seen at 450nm. is due to ferric iron.

Sapphire Spectra
SAPPHIRE - Greenish blue

Color is due to iron in the spectrum of the pale greenish blue sapphire used for this spectrum. A strong broad line showing at 450nm. combined with transmission in the remainder of the spectrum up to 690nm. indicates color is due to Fe3 rather than an Fe2-Ti4 transfer charge. However, the absence of prominent lines at 460nm. and 471nm. suggest the iron content is not high.

Sapphire Spectra
BLF0029

Color due to iron-titanium transfer charge and Fe3+-Fe3+ A dark blue sapphire shows a spectrum in which the three lines at 450nm; 460nm; and 471nm; have darkened and widened to merge as a single band. This plus the strong absorption due to the iron-titanium transfer charge produces a very dark blue which in some stones have a greenish overtone This is often seen in blue sapphire from Thailand.

Sapphire Spectra
SAPPHIRE - Padparadscha

Color due to chromium. This orangy-pink variety of sapphire, referred to by many as "Padparadscha", may show a weak chromium spectrum in which the usual absorption band in the green and lines in the blue maybe seen but can be weak and indistinct. However, by adjusting the lighting the emission lines at 693/694nm. can be seen to fluoresce strongly to indicate a presence of chromium

Jewelry Television acknowledges the significant scientific contributions of John S Harris, FGA to the study of gemstone spectra and with deep appreciation to him, acknowledges the use of his images and related notes about gemstones and their spectra in the educational materials on this website.

Countries of Origin

Tanzania, United Republic Of; Myanmar; Afghanistan; Viet Nam; Cambodia; Madagascar; Thailand; Mozambique; Pakistan; Unknown; Malawi; China; Russian Federation (the); Brazil; Nigeria; United States of America (the); Sri Lanka; Belize; Zambia; Kenya; Switzerland; French Polynesia; India; Norway; South Africa; Australia; Ethiopia

History

Sister stone to the ruby, most people think blue when they think sapphire. Blue is sapphire's best-known color. When sapphire is blue, it reminds us of the sky, the sea and eternity. But sapphire isn't always blue - we find sapphire in every color in, and under, the rainbow. One of the world's most prized stones is the orange sapphire known as padparadscha. It's lotus-flower color offers up fiery beauty. There are cool green sapphires, warm golden sapphires, pretty pink sapphires... in the world of the sapphire there's a color that's right for you. There is also a sapphire that changes color when moved from natural to incandescent light. It's color-change sapphire and it can be glorious! It can be a brilliant color change from blue to a rich purple or it may be a subtler change. Whether brilliant or subtle, the color-change of sapphire is compelling. Sapphire is corundum and a 9 on the hardness scale. It's wearable and wonderful. Sapphire is September's birthstone.

Care

Wear and enjoy your sapphires and be confident that you'll enjoy them for years to come. They are safe to clean in ultrasonic and steam cleaners.

Shop Sapphire

Related Videos

More About Sapphire

Sapphire is steeped in history and lore. It was believed that sapphire could protect kings from harm and envy; it is a symbol of trust, faithfulness, nobility, and royalty. The ancient Persians believed sapphire to be a chip off the pedestal on which the earth balances. Our favorite is the belief that sapphire can make a stupid man wise and transform a bad-tempered man into a good-tempered one. Why not follow the trend of some well-known royals and choose an engagement ring of sapphire? The colors are appealing, the folklore delightful and you'll be in very fine company!

Sapphire Gemstone

Sisk Gemology Reference

Showcasing 200 gemstones in over 1,000 pages and accompanied by more than 2,000 photos, The Sisk Gemology Reference is a must-have in every collector’s library. Each comprehensive, three-volume set features state-of-the-art photography, detailed illustrations, and scientifically precise descriptions to create an entrancing experience for gemstone amateurs and afficionados alike.

Shop Now

 

Creation Method

Lab Created Flux

Synthetic sapphire can be created in many ways, one of which is called flux growth. During the flux growth process, flux, a substance that reduces the melting point of surrounding material, is combined, in a metal-lined crucible, with the elements that make up a specific gem mineral. The crucible is heated until its contents are liquid and then it is allowed to cool very slowly. As cooling continues, the gem mineral crystallizes from the solution. Flux grown synthetic gems can take up to a year to grow to a facetable size, but the exceptional clarity of these gems is well worth the wait! Synthetic gems have the same chemical, optical, and physical properties of their natural counterparts, but are a more cost-effective alternative to a natural gem.

Lab Created Flux Sapphire
Lab Created Flux Classification
Common Name Lab Created Flux
Lab Created Flux Optical Properties
Fluorescence SWUV: weak to moderate chalky blue to blue-green to yellowish green
LWUV: inert
Lab Created Flux Characteristic Physical properties
Inclusions Platinum platelets from the crucible that appear metallic in reflected light but appear dark when stone is lit from behind. Flux is often white, brownish, yellow or orange but can be colorless. Flux inclusions can appear like natural fingerprint inclusions, wispy veils, comet tails, coarse globules of flux that can have a myriad of appearances from drippy, tubular or rod like or icicle looking, to clouds and minute particles, Stone might display angular growth zoning similar to natural.

Lab Created Flame Fusion

The flame fusion process for creating gems, also called the Verneuil process, is the most affordable and common synthesis method for producing corundum (ruby and sapphire) and spinel. Powdered chemicals (the building blocks of the gem) are dropped through a high-temperature flame. The molten powder repeatedly falls from the flame onto a rotating pedestal, creating a synthetic crystal, called a boule, which can later be faceted into a gemstone. Synthetic gems have the same chemical, optical, and physical properties of their natural counterparts, but are a more cost-effective alternative to a natural gem.

Lab Created Flame Fusion Sapphire
Lab Created Flame Fusion Classification
Common Name Lab Created Flame Fusion
Lab Created Flame Fusion Optical Properties
Fluorescence SWUV: weak to moderate chalky blue to blue-green to yellowish green
LWUV: inert
Lab Created Flame Fusion Characteristic Physical properties
Inclusions Might show face up color zoning, curved striae that crosses facet junctions and strings of gas bubbles that might be mistaken for needles. It might be possible to see Plato lines or twinning planes under magnification and immersion with polarized light. Sometimes heated with borax to created fingerprint like inclusions to mask curved striae. Stones might show colorless areas and uneven color distribution.

Lab Created Czochralski

Synthetic sapphire can be created in many ways, one of which is called the Czochralski method. During this process, the various elements that make up sapphire are melted in a platinum crucible. A small gem crystal (called a seed) attached to a rod is then dipped into the melt and slowly pulled away as the crystal grows around the seed. For this reason, the Czochralski method is also known as crystal pulling. Synthetic gems have the same chemical, optical, and physical properties of their natural counterparts, but are a more cost-effective alternative to a natural gem.

Lab Created Czochralski Sapphire
Lab Created Czochralski Classification
Common Name Lab Created Czochralski
Lab Created Czochralski Optical Properties
Fluorescence SWUV: Variable
LWUV: Variable
CCF Reaction Pink: weak red
Pleochroism Dichroic, moderate, varying shades of body color
Lab Created Czochralski Characteristic Physical properties
Inclusions Stones are almost always inclusion free. If internal characteristics are present they are gas bubbles, curved striae that is hard to see and smoke-like swirling veil-like inclusions.

Lab Created Floating Zone

One method of creating synthetic sapphire is called floating zone. In this method of gem synthesis, originally developed by engineers to create super pure silicon, a sintered rod of powdered material, comprised of elements necessary for the gem to grow, is heated with infrared radiation in a vacuum while the ends of the rod are rotated in opposite directions. Since all impurities including air are removed during crystallization, very clean crystals can form.

Lab Created Floating Zone Sapphire
Lab Created Floating Zone Classification
Common Name Lab Created Floating Zone
Lab Created Floating Zone Optical Properties
Fluorescence SWUV: moderate to strong red
LWUV: strong red
CCF Reaction Pink: weak red
Pleochroism Dichroic, moderate, varying shades of body color
Lab Created Floating Zone Characteristic Physical properties
Inclusions Stones are almost always inclusion free. If internal characteristics are present they are gas bubbles that are not perfectly round and swirls of color.

Lab Created Color-change

The flame fusion process for creating gems, also called the Verneuil process, is the most affordable and common synthesis method for producing corundum (ruby and sapphire) and spinel. Powdered chemicals (the building blocks of the gem) are dropped through a high-temperature flame. The molten powder repeatedly falls from the flame onto a rotating pedestal, creating a synthetic crystal,called a boule, which can later be faceted into a gemstone. Synthetic gems have the same chemical, optical, and physical properties of their natural counterparts, but are a more cost-effective alternative to a natural gem.

Lab Created Color-change Sapphire
Lab Created Color-change Classification
Common Name Lab Created Color-change
Lab Created Color-change Optical Properties
Dispersion Strength: weak fire Value: 0.018
Fluorescence SWUV: moderate orange to red or blue
LWUV: moderate orange to red
Pleochroism Dichroic, moderate violet to pinkish brown
Lab Created Color-change Characteristic Physical properties
Inclusions Flame fusion color-change sapphire might have bubbles and curved striae.

Lab Created Hydrothermal

Hydrothermally grown synthetic sapphires crystallize slowly out of a solution (a mix of water and dissolved elements) that has been exposed to heat and pressure similar to the conditions on Earth under which the natural gem mineral grows. Synthetic gems have the same chemical, optical, and physical properties of their natural counterparts, but are a more cost-effective alternative to a natural gem.

Lab Created Hydrothermal Sapphire
Lab Created Hydrothermal Classification
Common Name Lab Created Hydrothermal
Lab Created Hydrothermal Optical Properties
Fluorescence SWUV: Inert
LWUV: Inert
CCF Reaction If colored by chromium bright red
Lab Created Hydrothermal Characteristic Physical properties
Inclusions Look for chevron, wavy, zig-zag or mosaic growth patterns in hydrothermal synthetic ruby because stones might show growth zoning similar to natural ruby. Fingerprint like inclusions with 2-phase and 3-phase inclusions can be seen in stones. Sometimes flake like copper inclusions are visible in reflected light.

Optical Phenomena

Color Change

While color change sapphires come from a variety of locations, the gem gravels of Tanzania are the main source. Color change sapphires present gem lovers with an opportunity to own the rare and stunning color change effect in a gem other than alexandrite, garnet, spinel, tourmaline or diaspore. While the colors tend to vary depending on locale, in general they change from blue to purple. You can observe color change in this gem by viewing it interchangeably in natural and incandescent light.

Color Change Sapphire
Color Change Classification
Common Name Color Change
Color Change Optical Properties
Dispersion Strength: weak fire Value: 0.018
Fluorescence SWUV: Inert
LWUV: Inert
Pleochroism Dichroic, varies with bodycolor
Color Change Characteristic Physical properties
Inclusions This stone has a type II clarity. Color change sapphire sometimes have silk composed of rutile needles, dark brown crystals, boehmite or zircon crystals. Stones might have fingerprint or 2-phase inclusions. Hexagonal growth and strong color zoning are possible in some stones. Untreated stones will usually have inclusions intact. Heat treated stones will have fracture halos or snowballs around crystal inclusions(untreated stones from magmatic areas might also show these characteristics). Silk will be broken and might show sintered areas especially around the girdle.

Cat's-Eye

The term cat's eye, or chatoyancy, is used to describe a phenomenal optical property in gemstones, in this case sapphire. The effect, when present, appears as a bright, narrow slit similar to the pupils in the eyes of your favorite feline. This phenomenon is caused by parallel fibrous or needle-like inclusions that interfere with the passage of light through the crystal, scattering and reflecting light back to the viewer as a thin line.

Cat's-Eye Sapphire
Cat's-Eye Classification
Common Name Cat's-Eye
Cat's-Eye Optical Properties
Dispersion Strength: weak fire Value: 0.018
Fluorescence SWUV: Blue: Inert; possibly weak chalky blue or yellowish green this might indicate heat treatment Pink: weak orangy-red Orange: usually inert Yellow: weak red to orange-red Green: inert Violet: inert or weaker to moderate red Colorless: inert to moderate red to orange Brown: usually inert, maybe weak red Black: inert
LWUV: Blue: Inert; possibly red to orange Pink: strong orange-red Orange: maybe strong orange red Yellow: inert to moderate orange red to orange-yellow Green: inert Violet: inert to moderate to strong red Colorless: inert to moderate red to orange Brown: usually inert, maybe weak red Black: inert
Pleochroism Unobservable
Cat's-Eye Characteristic Physical properties
Inclusions Cat's-eye sapphire will have silk or sets of parallel rutile needles, hexagonal growth lines, color zoning, liquid , negative and mineral inclusions. Some stone might show twinning.

Star

Star sapphire exhibits the optical phenomenon called asterism, a star-like pattern created on the surface of a gemstone when light encounters parallel fibrous, or needle-like, inclusions within its crystal structure. Light that strikes the inclusions within the gem reflects off of the inclusions, creating a narrow band of light. When two or more intersecting bands appear, a star pattern is formed. Depending on the crystal, the star typically has six rays, but on occasion, twelve rays.

Star Sapphire
Star Classification
Common Name Star
Star Optical Properties
Dispersion Strength: weak fire Value: 0.018
Fluorescence SWUV: Inert to strong red
LWUV: Inert to strong red
Pleochroism Unobservable
Star Characteristic Physical properties
Inclusions Star sapphires will have silk or sets of parallel rutile needles that produce a 6-ray star, hexagonal growth lines, color zoning and mineral inclusions. Weak and less well formed stars along with weaker body color is typical of natural stones. In natural stones at least one ray of the start will be perpendicular to the hexagonal growth zones. Stone with 12-rayed stars are rare but typically occur in dark blue or black stones.

Lab Created Star

Synthetic star sapphire exhibits the optical phenomenon called asterism, a star-like pattern created on the surface of a gemstone when light encounters parallel fibrous, or needle-like, inclusions within its crystal structure. Light that strikes the inclusions within the gem reflects off of the inclusions, creating a narrow band of light. When two or more intersecting bands appear, a star pattern is formed. The flame fusion process for creating gems, also called the Verneuil process, is the most affordable and common synthesis method for producing corundum (ruby and sapphire) and spinel. Powdered chemicals (the building blocks of the gem) are dropped through a high-temperature flame. The molten powder repeatedly falls from the flame onto a rotating pedestal, creating a synthetic crystal, called a boule, which can later be faceted into a gemstone. Synthetic gems have the same chemical, optical, and physical properties of their natural counterparts, but are a more cost-effective alternative to a natural gem.

Lab Created Star Sapphire
Lab Created Star Classification
Common Name Lab Created Star
Lab Created Star Optical Properties
Dispersion Strength: weak fire Value: 0.018
Fluorescence SWUV: inert to moderate chalky blue to yellowish green
LWUV: Inert
Pleochroism Unobservable
Lab Created Star Characteristic Physical properties
Inclusions Flame fusion stones might display curved growth and a unusually display a centered and well defined 6-rayed star. The curved growth is especially visible on the flat base of the stone. The stones might have gas bubbles and minute rutile needles that make up the star will confined to the surface of the stones.

Enhancement

Cobalt-Lead Glass Filled

Cobalt-lead glass filled sapphire has been filled through a process similar to "infilling" using lead glass. Performed at low heat, this is a less durable treatment and should be treated gently, avoiding household and professional chemicals. This treatment, which uses cobalt-colored lead glass, improves clarity, color, and may add weight through the filling of voids and fissures.

Cobalt-Lead Glass Filled Sapphire
Cobalt-Lead Glass Filled Classification
Common Name Cobalt-Lead Glass Filled
Cobalt-Lead Glass Filled Optical Properties
Fluorescence SWUV: inert
LWUV: inert
CCF Reaction red
Pleochroism Dichroic, violet blue and greenish blue
Cobalt-Lead Glass Filled Characteristic Physical properties
Inclusions Cobalt-lead glass filled sapphire will have gas bubbles and will display purplish red flash colors from the lead glass filling. There will be color concentrations in the fissures of the stone.
Stability Poor
Tim Matthews

Author

Tim Matthews

Tim Matthews is President and Chief Executive Officer of Jewelry Television® (JTV), as well as a member of the company's Board of Directors. He oversees and leads all aspects of the company's powerful omni-digital retail platform that uniquely specializes in fine jewelry and gemstones. His passion for business and gemstones has led him to become a recognized expert in the field of gemology. He is a life member of the Gemmological Association of Great Britain (Gem-A) and has earned Gem-A's highest degrees, the Gemmology (FGA) and Diamond (DGA) diplomas. He is also a Graduate Gemologist (GG) of the Gemological Institute of America (GIA) and has also completed GIA's Graduate Diplomas in Diamonds, Colored Stones and Pearls. Under his leadership, JTV has become the leader in the sourcing and selling of color gemstones and jewelry.

This page was created on June 27, 2014.

This page was last edited on October 24, 2019.