Natural Star Sapphire in Bangkok: Blue and Black Star Sapphire from JTC Silom
By Ansh Gupta, second generation at KC Gems House, Jewelry Trade Center, Silom Road, Bangkok
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Alt: A natural blue star sapphire cabochon showing a sharp six-rayed star under a single light in Bangkok
Hold a good star sapphire under a single light and turn it slowly. A six-rayed star appears on the surface, glides across the dome as you move, and snaps back to the centre when you hold it still. Nothing else in jewellery does that, and nothing else is so easy to fake, which is why buying a star sapphire well takes a bit of knowledge.
Thailand has a special relationship with this stone. The basalt gem fields of eastern Thailand produced black star sapphire for decades, Thai cutters are some of the best cabochon cutters in the world, and Bangkok is where much of the world’s natural star sapphire from Sri Lanka and Burma is traded.
My family has traded coloured stones in Bangkok since 1990, from our office inside the Jewelry Trade Center on Silom Road, minutes from the GIT, AIGS and Lotus Gemology laboratories. This page explains how a star forms, how to judge it, how to tell natural stars from synthetic and diffused ones, what star sapphire costs per carat in 2026, and how to buy it safely in Bangkok. If you already know what you want, jump to how to buy star sapphire from us or see the full natural gemstones collection.
Star sapphire at a glance
Mineral — Corundum (aluminium oxide, Al2O3), the same as all sapphire and ruby
Hardness — 9 on the Mohs scale
Phenomenon — Asterism: a six-rayed star (rarely twelve)
Cause of the star — Fine needle inclusions (“silk”), usually rutile, aligned in three directions
Cut — Cabochon (domed, polished, unfaceted)
Main colours — Blue, grey-blue, black, purple, pink, white; red stars are star rubies
Key origins — Sri Lanka, Myanmar (Burma), Thailand, Australia, Madagascar, Tanzania
Typical treatment — Usually unheated; diffusion and synthetic stars must be disclosed
Birthstone — September (sapphire)
Thai name — ไพลินสาแหรก, สตาร์แซฟไฟร์
How a star sapphire gets its star
All sapphire is corundum. As some sapphire crystals grow and cool, tiny needles of rutile (titanium dioxide) and sometimes hematite or ilmenite form inside them. Because corundum is a hexagonal crystal, those needles line up in three directions, 120 degrees apart. Gemmologists call these needles “silk”.
When a cutter shapes the crystal into a smooth dome with the base parallel to the crystal’s main axis, light reflecting off the three sets of needles forms three bands of light that cross in the middle. Three bands make six rays: the star. The effect is called asterism.
A few things follow from this:
1. A star needs silk. Heavy silk makes a strong star but reduces transparency. The best stars balance a sharp star with good colour and some translucency.
2. A star needs a dome. Star sapphires are always cut as cabochons. The height and symmetry of the dome decide how sharp and centred the star looks.
3. Heat destroys stars. High-temperature heating, used on most faceted sapphire, dissolves the silk and removes the star. That is why most natural star sapphires have never been heated, a big plus for buyers who want untreated stones.
Very rarely, two different types of needles create two overlapping stars, giving a twelve-rayed star. These are collector stones.
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Alt: A star sapphire cabochon photographed under a penlight showing the six-rayed star centred on the dome
Famous star sapphires
• The Star of India, about 563 carats, is a grey-blue star sapphire from Sri Lanka in the American Museum of Natural History in New York. It is one of the largest known star sapphires.
• The Star of Bombay, about 182 carats, is a violet-blue Sri Lankan star sapphire at the Smithsonian Institution in Washington.
• The Black Star of Queensland, about 733 carats, is a black star sapphire found in Australia in the 1930s and one of the most famous black stars in the world.
Star sapphire colours
Blue star sapphire
The classic. Fine blue star sapphire has a medium to medium-dark blue body colour, a sharp silvery white star, and some translucency so the colour glows rather than looking flat grey. Sri Lanka (Ceylon) produces lighter, brighter blue stars; Burma produces deeper, richer blue stars with a velvety look. Grey-blue stars are much more common and much cheaper.
Black star sapphire
Black star sapphire is the star sapphire Thailand is best known for. It has a very dark brown to black body and usually a golden or bronze star, because the star often comes from hematite and ilmenite rather than only rutile. Thai black star sapphire came mainly from the basalt gem fields of eastern Thailand around Chanthaburi, and Australia is the other main source. Black star sapphire is affordable, durable and very popular in men’s rings and Thai lucky jewellery.
Purple, pink and white star sapphire
Violet, purple and pink star sapphires, mostly from Sri Lanka and Burma, are increasingly popular for women’s jewellery. White and grey star sapphires are the most affordable stars and can show very sharp, bright stars.
Star ruby
When the corundum is red, the stone is a star ruby. Burmese star rubies are prized. Be careful in this category: many low-cost “star rubies” in tourist markets are heavily fractured stones filled with glass. We cover this in the treatment section below.
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Alt: A row of natural star sapphire cabochons in blue, black with a golden star, purple, pink and white
How to judge a star sapphire
When I grade a star sapphire I look at the star first and the body colour second. Here is the checklist.
1. Star sharpness
The rays should be thin, bright and well defined, not fuzzy or blurred. Hold the stone under a single light source, such as a penlight or the sun. A fluorescent tube or several lights at once make every star look weaker.
2. Star centring
When you look straight down on the stone, the star should sit in the centre of the dome. An off-centre star is a cutting fault and lowers the price.
3. Complete, straight rays
All six rays should be present, straight, and run all the way down the dome toward the base. Missing or broken rays, or rays that bend, reduce value.
4. Movement
A good star glides smoothly across the dome as you move the light and returns to the centre. This rolling movement is part of the beauty.
5. Body colour
A fine blue body with a sharp star is worth much more than a grey body with the same star. For black stars, a clean, even black with a bright golden star is the goal.
6. Translucency
Most star sapphires are translucent to semi-opaque. A stone with a little translucency, so the colour glows, is more valuable than a flat, opaque stone.
7. Cut and proportions
The dome should be symmetrical and not too flat (weak star) or too high (bulky in jewellery). Many native-cut stars carry a heavy, thick base to save weight. Some weight in the base is normal, but a very heavy base makes the stone sit high and adds carats you pay for without seeing.
Natural, synthetic and treated star sapphires
This is where most buyers get caught. Here are the main things you will meet in Bangkok and around the world.
Natural, unheated star sapphire
The real thing. Natural silk, natural star, usually no heat. The star is rarely perfect: it may be slightly uneven, the body may have colour zoning, and you may see small inclusions. Those imperfections are actually a sign of a natural stone.
Synthetic star sapphire
Synthetic star sapphire and star ruby were first made in the late 1940s and sold widely as “Linde stars”. They have perfect, very sharp, very evenly spaced stars, very even colour and often curved growth lines visible under magnification. A star that looks too perfect, at a low price, is a warning sign. Synthetics are fine when sold as synthetic but should never be sold as natural.
Diffusion-treated stars
Some stones have their star created or strengthened by diffusing titanium into the surface layer under heat. The star sits only in a thin skin on the surface and often looks unnaturally sharp and uniform. A gem laboratory can identify diffusion treatment, and it must be disclosed. Diffused star stones are worth a fraction of natural stars.
Glass-filled star rubies
Low-grade, heavily fractured ruby is often filled with lead glass to hide the fractures and improve the look. Many cheap “star rubies” in tourist shops are made this way. Glass-filled stones are fragile, can be damaged by jewellery repair and household chemicals, and have very low value. They must be disclosed as glass-filled.
Dyed and coated stones
Occasionally low-grade stones are dyed or coated to improve colour. Rare in quality star sapphire, but another reason to buy from a dealer who puts the treatment in writing.
Our rule: every star sapphire on our desk is described in writing as natural or synthetic, and treated or untreated, before you pay. For any important stone, we recommend a report from GIT or AIGS, both a short walk from our office at JTC. You can read about how labs work in our article on what gemmology schools see when they grade a stone.
Where the best star sapphire comes from
Sri Lanka — Bright light to medium blue, grey-blue and violet stars; many famous large stars
Myanmar (Burma) — Rich, deep blue stars and fine star rubies
Thailand — Black star sapphire with golden stars from the eastern gem fields
Australia — Black and dark blue star sapphire, including the Black Star of Queensland
Madagascar and Tanzania — Blue, grey and coloured stars
India — Grey and black stars, plus historic material
Origin matters more for blue stars than black. A laboratory can often state Sri Lankan or Burmese origin for a fine blue star, and that report adds value.
Star sapphire price per carat in 2026
These are typical Bangkok retail ranges for natural, untreated star sapphire cabochons from about 2 to 10 carats with a complete, reasonably centred star. Exceptional stars, rare colours and laboratory origin reports cost more.
Black star sapphire, Thai or Australian — $10 to $80
White and grey star sapphire — $30 to $200
Grey-blue star sapphire, commercial — $50 to $400
Purple and pink star sapphire — $200 to $2,000
Fine blue star sapphire, Sri Lanka — $800 to $5,000
Fine blue star sapphire, Burma — $1,500 to $8,000+
Fine natural star ruby — $500 to $5,000+
Synthetic star sapphire (for comparison) — $1 to $20
What moves the price:
1. The star. Sharpness, centring and completeness can double or halve the value.
2. Body colour. A true blue is worth many times a grey.
3. Origin. Burma and Sri Lanka carry premiums for blue.
4. Size. Fine stars become rare above ten carats.
5. Treatment. Untreated natural stars are worth far more than diffused, glass-filled or synthetic stones.
Faceted sapphire prices work very differently because of heat treatment. Our natural vs lab sapphire price calculator shows how treatment and size change faceted sapphire prices.
What your budget buys in star sapphire
• Under $200: A good Thai black star sapphire of three to eight carats with a sharp golden star, ideal for a men’s ring.
• $200 to $1,000: A grey-blue or white star sapphire with a sharp star, or a pretty purple star of two to four carats.
• $1,000 to $5,000: A Sri Lankan blue star of two to four carats with good colour and a sharp, centred star.
• $5,000 to $20,000: A fine Sri Lankan or Burmese blue star of four to ten carats, often with a laboratory origin report.
• Over $20,000: Collector stars with exceptional colour and sharpness, twelve-rayed stars, and large Burmese stones.
Star sapphire vs faceted sapphire
Look · Star sapphire: Soft glow with a moving six-rayed star · Faceted blue sapphire: Bright sparkle from facets
Usual treatment · Star sapphire: Usually unheated · Faceted blue sapphire: Most are heated
Price for similar colour and size · Star sapphire: Generally lower · Faceted blue sapphire: Generally higher
Durability · Star sapphire: 9 Mohs, very tough cabochon · Faceted blue sapphire: 9 Mohs, facet edges can chip in hard knocks
Best for · Star sapphire: Men’s rings, vintage designs, collectors, people who want untreated stones · Faceted blue sapphire: Engagement rings, classic sparkle
If you love sapphire but want something more unusual, untreated and often better value, a star sapphire is worth a serious look. If you want the classic sparkle of a faceted stone, see our corundum catalogue and our article on the Gemports Award 2026 ruby and sapphire winners to see what top faceted sapphire looks like.
From mine to Bangkok: how star sapphire reaches JTC
Most star sapphire rough comes from gem gravels in Sri Lanka, Myanmar, Madagascar and East Africa, and historically from the basalt fields of eastern Thailand and Queensland in Australia. Miners and rough dealers sort silky material that will not make good faceted stones and set it aside for cabochons.
That rough comes to Thailand, where cabochon cutters in Chanthaburi and Bangkok decide how to orient each piece so the star sits in the centre. This is skilled work. A cutter who reads the silk correctly can turn an ordinary-looking piece of rough into a stone with a sharp, centred star. A cutter who misreads it produces an off-centre star that loses half its value.
Finished stars reach the offices of the Jewelry Trade Center and the dealers of Silom and Mahesak Road, where buyers from Hong Kong, India, Europe and the Middle East compete for the best stones. Buying here puts you at the end of that chain without the retail markups added abroad.
Common star sapphire buying mistakes
1. Judging the star under shop lights. Multiple lights soften every star, and strong spotlights can make a weak star look good. Use one light, then daylight.
2. Paying natural prices for synthetic stars. Old “Linde” style synthetics still circulate, often in vintage jewellery. Ask for natural in writing.
3. Buying a glass-filled star ruby as a natural one. Cheap star rubies are very often glass-filled. They can be pretty, but the price should reflect it.
4. Ignoring the base. A very thick base adds weight and price without adding beauty, and makes the ring sit high.
5. Choosing a setting that covers the dome. Heavy prongs block the rays. The star needs an open dome to move.
6. Expecting perfection. A perfect star is often a sign of a synthetic. Slight unevenness is normal in natural stones.
How to buy star sapphire safely in Bangkok
1. Always look under a single light. Bring a phone torch. Check the star in direct sunlight too.
2. Turn the stone. The star should move smoothly and return to the centre.
3. Be suspicious of perfection. A flawless, razor-sharp star on an even body at a low price is often synthetic.
4. Ask for natural and untreated in writing. Especially for star rubies, ask specifically whether the stone is glass-filled.
5. Get a report for any important stone. GIT, AIGS and Lotus Gemology are all near JTC.
6. Never buy from a shop a stranger takes you to. The classic Bangkok gem scam often involves “special” star sapphires and star rubies.
7. Never buy to resell. Nobody honest will tell you to double your money back home.
For more, read why Bangkok is one of the world’s best places to buy gemstones and our how to buy page.
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Alt: A men’s 18k gold ring set with a Thai black star sapphire showing a golden six-rayed star
Buying a star sapphire remotely
Star sapphires are harder to judge on a screen than faceted stones, because the star depends on the light. When clients buy from abroad, this is what we send and what you should ask any dealer for:
1. A single-light video. A phone torch moved slowly across the stone, showing the star gliding and returning to the centre.
2. A daylight video. The stone turned in indirect daylight near a window, to show the true body colour.
3. A side view. A clear photo or video of the profile, so you can see the dome height and how thick the base is.
4. Measurements and weight. Length, width and depth in millimetres, plus carat weight, so your setting can be designed properly.
5. The treatment statement and any report. Natural or synthetic, treated or untreated, and a GIT or AIGS report for important stones.
If a dealer cannot or will not send these, keep looking.
Why buy star sapphire from us
There are many honest star sapphire dealers in Bangkok. Here is how we work.
• Family trade since 1990. KC Gems House was built by my father, KC Gupta, who began trading coloured stones in Bangkok in 1990. I am the second generation. Read more on our family business page and my page.
• Inside JTC, at trade level. Our office is in the Jewelry Trade Center on Silom Road, where the professional trade buys.
• Natural, in writing. Every star sapphire is invoiced as natural or synthetic, and treated or untreated. We do not sell glass-filled stones as anything other than glass-filled.
• We show you the star properly. Single-light videos for remote buyers, and daylight viewing at our office.
• Reports on request. GIT and AIGS are minutes away; AIGS is in the same building.
• Set here. We set star sapphires in 10k, 14k and 18k gold, with settings designed to show the star. See custom jewellery in Bangkok or start a custom order. For men’s designs, see our men’s jewellery.
• Worldwide shipping. Insured shipping to the UK, Europe, the US, the Middle East and beyond.
Star sapphire jewellery ideas
• Men’s rings. A black star or grey-blue star sapphire in a heavy gold signet or gypsy ring is a classic. Star sapphire is 9 on the Mohs scale, so it handles daily wear.
• Solitaire rings. A blue star sapphire in a simple bezel or four-prong setting lets the star move freely.
• Halo rings. A ring of small diamonds or white sapphires around a blue star adds sparkle to contrast with the soft glow of the cabochon.
• Pendants. A star sapphire pendant catches light as it moves.
• Vintage designs. Star sapphires were hugely popular from the 1930s to the 1960s. They suit milgrain and Art Deco settings like our Art Deco milgrain ring.
Setting tips for star stones
• Leave the dome open. Prongs or bezels that cover too much of the dome block the star.
• Mount it level. The base should sit flat so the star appears in the centre when the ring is worn.
• Think about the base. Thick-based native cuts need a deeper setting. We measure every stone before designing the mount.
Caring for star sapphire
• Durability: At 9 on the Mohs scale, star sapphire is one of the toughest coloured stones for daily wear.
• Cleaning: Warm water, mild soap and a soft brush. Avoid ultrasonic cleaning for star rubies and any fracture-filled stone.
• Glass-filled stones: Keep away from lemon juice, household cleaners and jeweller’s torches. Tell any jeweller before repair.
• Storage: Store separately from diamonds, which can scratch the dome.
Star sapphire and Thai belief
Thai buyers have long valued star stones. In Thai, a star stone is often called พลอยสาแหรก, from สาแหรก, the net of cords used to carry pots, because the crossed rays look like those cords. Star sapphire belongs to the blue sapphire (ไพลิน) family, one of the nine nopphakao stones. Black star sapphire is especially popular in Thai men’s jewellery and is often worn for protection and steadiness.
Star sapphire for wholesale buyers
We supply black star sapphire in calibrated cabochon sizes, matched pairs for earrings and cufflinks, and single fine blue stars. Tell us the colour, sizes, quantity and budget and we will prepare a selection with single-light videos. See our wholesale page.
ไพลินสาแหรก และสตาร์แซฟไฟร์แท้ ที่ JTC สีลม
สตาร์แซฟไฟร์ หรือไพลินสาแหรก คือแซฟไฟร์ธรรมชาติที่มีเส้นแสงรูปดาวหกแฉกปรากฏบนผิวพลอยเมื่อส่องด้วยไฟดวงเดียว ดาวเกิดจากเส้นแร่รูไทล์ขนาดเล็กที่เรียงตัวอยู่ในเนื้อพลอย จึงต้องเจียระไนแบบหลังเบี้ย (คาโบชอง) เท่านั้น
สตาร์แซฟไฟร์ธรรมชาติส่วนใหญ่ไม่ผ่านการเผา เพราะความร้อนสูงจะทำให้ดาวหายไป ประเทศไทยเป็นแหล่งของสตาร์แซฟไฟร์สีดำที่มีดาวสีทองจากแหล่งพลอยในภาคตะวันออก ส่วนสตาร์แซฟไฟร์สีน้ำเงินคุณภาพดีมาจากศรีลังกาและพม่า
ควรระวังสตาร์แซฟไฟร์สังเคราะห์ที่มีดาวคมชัดสมบูรณ์เกินจริง สตาร์ที่ผ่านการแพร่ซึมไทเทเนียม และทับทิมสาแหรกที่อุดแก้ว ซึ่งต้องแจ้งให้ลูกค้าทราบทุกครั้ง
เราคือ KC Gems House ค้าพลอยในกรุงเทพฯ มาตั้งแต่ปี 1990 สำนักงานอยู่ในอาคาร Jewelry Trade Center ถนนสีลม เราแจ้งว่าพลอยเป็นของธรรมชาติหรือสังเคราะห์ และผ่านการปรับปรุงคุณภาพหรือไม่ เป็นลายลักษณ์อักษรก่อนชำระเงิน ส่งตรวจใบรับรองจาก GIT หรือ AIGS ได้ และรับทำแหวนผู้ชาย แหวนผู้หญิง และจี้ ด้วยทอง 10K 14K และ 18K
Frequently asked questions about star sapphire
What makes a star sapphire valuable?
A sharp, centred, complete six-rayed star; a strong body colour (fine blue is worth most); some translucency; a well-proportioned dome; natural origin with no diffusion, glass filling or synthetic growth; and a respected origin such as Sri Lanka or Burma for blue stars.
How do I know if a star sapphire is real?
Natural stars are rarely perfect. They often have slightly uneven rays, colour zoning and small inclusions. Synthetic stars usually look too sharp and too even, with very uniform colour. The safest way is a report from a laboratory such as GIT, AIGS or Lotus Gemology in Bangkok.
How much does a star sapphire cost per carat?
In Bangkok, Thai black star sapphire runs about $10 to $80 per carat, grey-blue commercial stars about $50 to $400, and fine Sri Lankan or Burmese blue stars from about $800 to $8,000 or more per carat.
Is star sapphire heat treated?
Most natural star sapphires are not heated, because high heat dissolves the silk that creates the star. Some stones receive low-temperature heat or diffusion treatment, which must be disclosed.
Where is black star sapphire from?
Black star sapphire comes mainly from the basalt gem fields of eastern Thailand and from Australia. It usually has a golden or bronze star.
Can you wear a star sapphire every day?
Yes. Star sapphire is corundum, 9 on the Mohs scale, so it is one of the most durable coloured gemstones for daily wear. Glass-filled star rubies are the exception; they need much more care.
What is a twelve-ray star sapphire?
A rare star sapphire with two sets of needle inclusions that create two overlapping six-rayed stars. Twelve-ray stars are collector stones.
Why does my star sapphire’s star look weak indoors?
Stars show best under a single, direct light source such as sunlight or a spotlight. Diffuse lighting from many sources makes every star look softer. It does not mean the stone is poor.
What is a star sapphire called in Thai?
Star sapphire is often called ไพลินสาแหรก or สตาร์แซฟไฟร์ in Thai. Star stones in general are called พลอยสาแหรก.
Do you ship star sapphire internationally?
Yes. We send single-light and daylight videos before payment and ship insured worldwide.
Talk to us about star sapphire
Tell us the colour, size and budget you have in mind, and we will send single-light videos of real stones with treatment information. Visit us at JTC, or buy remotely.
Ask about a star sapphire
Explore other natural stones: spinel, garnet, zircon, pink and padparadscha sapphire, tourmaline, amethyst and citrine and cat’s eye chrysoberyl. Or go back to all natural gemstones.