# Star ruby

- Page: https://taslar.bumba.tr/en/stones/star-ruby/
- Turkish: Yıldız yakut
- Kind: Variety
- Classification: Minerals › Oxides and hydroxides
- Chemical formula: Al₂O₃
- Crystal system: Trigonal
- Hardness (Mohs): 9
- Specific gravity: 3.98–4.1 g/cm³
- Refractive index: 1.759–1.772
- Lustre: Adamantine, Vitreous (glassy)
- Transparency: Transparent, Translucent, Opaque
- Colours: red, pinkish red, purplish red, deep maroon
- Streak: White
- Cleavage: None; may show parting that resembles cleavage
- Fracture: Uneven to conchoidal
- Value ladder: 7/9 step, Precious stone

A ruby that shows a six-rayed star of light when cut as a dome, produced by fine rutile needles inside it.

Star ruby is ruby containing extremely fine rutile needles aligned in particular directions, so that when it is cut as a dome (cabochon) it shows a six-rayed star on its surface. The effect is called asterism. Star rubies are mostly translucent to opaque. The most famous come from Myanmar and Sri Lanka, and opaque, deep maroon star rubies also come from southern India.

## How does it form?

Like other rubies, star ruby is [corundum](/en/stones/corundum/) coloured red by chromium. What sets it apart is that the crystal contains very fine needles of rutile (titanium oxide), which gemmologists call “silk”. Because of corundum's crystal structure, these needles line up in three directions. Each set of needles reflects light into a bright band, and where the three bands meet a six-rayed star appears. With too few needles no star shows; with too many the stone becomes cloudy and loses its transparency.

Rubies form mainly in marbles and in basalt-related rocks. The Mogok valley of Myanmar is known for its marble-hosted rubies, while in Sri Lanka star ruby turns up in the gem gravels together with star sapphire.

## What is it used for?

- **Jewellery:** Cut as a dome, it is set in rings, necklaces and earrings; its hardness suits everyday wear.
- **Collections and museums:** Large stones such as the Rosser Reeves and DeLong star rubies are on display in museums in Washington and New York.
- **Gemmology:** Telling natural stars from synthetic ones is a frequent task for gem laboratories.

## The quality of the star

In a good star ruby the six rays are sharp, straight and equally long, and meet exactly in the middle of the dome. To achieve this the cutter orients the dome perpendicular to the main axis of the crystal (the c-axis). The Rosser Reeves Ruby, too, was repolished to centre its star. According to Wikipedia, star ruby, found now and then with star sapphire in Sri Lanka, ranks among the most valued “fancy stones”.

## Star ruby or star sapphire?

Ruby and sapphire are the same mineral; only the colour decides the name. As the chromium that makes it red decreases, the stone turns pink and at some point counts as pink sapphire. Because the boundary between red and pink can differ from one laboratory to another, a pinkish stone with a star may be called a “star ruby” in one place and a “pink star sapphire” in another. The same Sri Lankan gravels yield both star ruby and blue, purple and grey [star sapphires](/en/stones/star-sapphire/).

## How to recognise it

- A dome-cut red stone shows a six-rayed star; as the light or the stone moves, the star glides across the surface. It shows best under a single point of light (sunlight, a torch).
- Being a ruby, it is very hard (Mohs 9) and heavy for its size.
- In natural stones the star is often not perfectly sharp and the colour is slightly hazy. A very sharp star and an overly even, almost transparent red can point to a synthetic.
- A firm identification, especially telling natural from synthetic, needs a gem laboratory.

## Fakes and imitations

- Synthetic star ruby: using the method developed at the Linde company in the United States in 1947, titanium-bearing synthetic corundum is grown and then heated to form rutile needles inside it. Linde made synthetic star rubies as well as star sapphires.
- GIA has documented large laboratory-grown star rubies and sapphires given their star by titanium diffusion into the surface.
- The reddish, sparkly stone sold in Türkiye as “yıldız taşı” (star stone) is not ruby but a man-made glass glittering with metal flakes.

## What determines its value?

The quality of the star and the body colour together set the value: the six rays should be sharp, straight and centred on the stone, and the colour a vivid, saturated red. Transparency matters too: translucent, brightly coloured stones are more sought after than opaque, very dark ones. Symmetry of the cut, size, treatments and origin also count. Because synthetic star rubies have been made for a long time, a laboratory report is decisive.

This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.

## Myths and misconceptions

- Myth: The red, sparkly stone sold in Türkiye as “yıldız taşı” is a kind of star ruby. Fact: The stone sold as “yıldız taşı” is a man-made glass sparkling with metal flakes, traced back to 17th-century Italy (known in English as goldstone). Star ruby is natural corundum that shows a six-rayed star of light when cut as a dome.
- Myth: Every ruby that shows a star is natural. Fact: Synthetic star ruby has been made since the late 1940s, and in some laboratory-grown stones the star is added by diffusing titanium into the surface. Telling a natural stone from a synthetic with certainty is a job for a laboratory.

## What is it believed to be good for?

This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.

- The mineralogist George F. Kunz (1913) writes that Eastern peoples believed stones showing a play of light, such as star ruby and star sapphire, brought good fortune to the wearer.
- In Kunz's list of wedding anniversary stones, star ruby is given for the 52nd year; he notes that for these multiples of thirteen the stone was believed to counteract the unlucky influence of the number.
- The American advertising executive Rosser Reeves carried the star ruby he later gave to the Smithsonian as a lucky stone, calling it “his baby”.

What science says: There is no scientific evidence that star ruby brings good fortune or cancels out unlucky numbers. The star is a physical effect produced by light reflecting from rutile needles aligned in three directions inside the stone, and it can also be made in a laboratory.

## Did you know?

- The 138.7-carat Rosser Reeves Ruby at the Smithsonian is considered one of the largest and finest star rubies in the world. It was repolished to centre the star and remove scratches, so it originally weighed just over 140 carats.
- The 100.32-carat DeLong Star Ruby at the American Museum of Natural History in New York was stolen together with the Star of India in the famous 1964 heist; it was recovered in 1965 from a phone booth at a highway service plaza in Florida.
- Around Channapatna in the Indian state of Karnataka, star ruby is dug not from mines but from the soil of mango and coconut orchards.

## Where is it found?

- Mogok, Mandalay Region, Myanmar (Major deposit): Gemdat lists many mines in the Mogok valley as star ruby localities; the 100.32-carat DeLong Star Ruby was found in Burma in the 1930s
- Ratnapura, Sabaragamuwa, Sri Lanka (Major deposit): Found with star sapphire in the gem gravels; the 138.7-carat Rosser Reeves Ruby at the Smithsonian is from Sri Lanka
- Yên Bái Province (Lục Yên area), Vietnam (Known locality): Gemdat lists Yên Bái Province as a star ruby locality
- Channapatna, Karnataka, India (Known locality): Opaque, deep maroon star ruby, dug not from mines but from the red and yellow soils of mango and coconut orchards

## Sources

- [Star Ruby (gem)](https://www.gemdat.org/gem-30582.html), Gemdat.org
- [Asterism (gemology)](https://en.wikipedia.org/wiki/Asterism_(gemology)), Wikipedia
- [Gem News International: Indian ruby mining, Gems & Gemology 50(1)](https://www.gia.edu/gems-gemology/spring-2014-gemnews-indian-ruby-mining), GIA, 2014
- [Ruby Description (Gem Encyclopedia)](https://www.gia.edu/ruby-description), GIA
- [Synthetic Star Sapphires and Rubies Produced by Wiede's Carbidwerk, Freyung, Germany (Schmetzer, Gilg, Bernhardt), Gems & Gemology 53(3)](https://www.gia.edu/gems-gemology/fall-2017-synthetic-star-sapphires-rubies), GIA, 2017
- [Lab Notes: Large laboratory-grown star ruby and sapphire, Gems & Gemology 55(3)](https://www.gia.edu/gems-gemology/fall-2019-labnotes-large-laboratory-grown-star-ruby-and-sapphire), GIA, 2019
- [Rosser Reeves Ruby](https://en.wikipedia.org/wiki/Rosser_Reeves_Ruby), Wikipedia
- [DeLong Star Ruby](https://en.wikipedia.org/wiki/DeLong_Star_Ruby), Wikipedia
- [The Curious Lore of Precious Stones (G. F. Kunz)](https://www.gutenberg.org/ebooks/57978), J. B. Lippincott Company (Project Gutenberg), 1913
- [Yıldız taşı faydaları: Yıldız taşı özellikleri nelerdir, ne işe yarar?](https://www.sabah.com.tr/saglik/2022/07/22/yildiz-tasi-faydalari-yildiz-tasi-ozellikleri-nelerdir-ne-ise-yarar), Sabah, 2022
- [Channapatna](https://en.wikipedia.org/wiki/Channapatna), Wikipedia


Source: https://taslar.bumba.tr/en/stones/star-ruby/ · Licence: CC BY-SA 4.0