The Navratna — "nine gems" — is the traditional set of stones that Indian astrology associates with the nine celestial bodies of the Jyotish system. Whatever one's view of that association, the set has shaped the Indian gem trade for centuries: these nine stones account for a large share of what is bought for wearing rather than for ornament, and each has a well-established list of substitutes, look-alikes and outright imitations.
This guide sets out the nine, the stones most often sold in their place, and what a laboratory test settles. It does not evaluate the astrological claims; identity is the laboratory's business, effect is not.
The nine and their associations
| Gem (Sanskrit / Hindi) | Mineral | Traditional association |
|---|---|---|
| Ruby (Manik / Manikya) | Corundum, red | Sun (Surya) |
| Pearl (Moti / Mukta) | Calcium carbonate, organic | Moon (Chandra) |
| Red coral (Moonga / Praval) | Calcium carbonate, organic | Mars (Mangal) |
| Emerald (Panna / Marakata) | Beryl, green | Mercury (Budh) |
| Yellow sapphire (Pukhraj / Pushparaga) | Corundum, yellow | Jupiter (Guru / Brihaspati) |
| Diamond (Heera / Vajra) | Carbon | Venus (Shukra) |
| Blue sapphire (Neelam / Indraneela) | Corundum, blue | Saturn (Shani) |
| Hessonite (Gomed / Gomedhaka) | Grossular garnet, orange-brown | Rahu |
| Cat's eye (Lehsunia / Vaidurya) | Chrysoberyl with chatoyancy | Ketu |
Three of the nine are corundum in different colours; two are organic; one is a garnet; one is a beryl; one is chrysoberyl; one is diamond. That mineralogy is what the laboratory actually tests.
What is sold in their place
For each of the nine there is a hierarchy of substitution, from honest to deceptive.
Honest substitutes (Upratna). Tradition itself provides lower-cost alternatives: red garnet or red spinel for ruby, moonstone for pearl, carnelian for coral, peridot or green tourmaline for emerald, citrine or yellow topaz for yellow sapphire, white sapphire or zircon for diamond, amethyst or iolite for blue sapphire, other orange garnets for hessonite, and quartz or apatite cat's eye for chrysoberyl cat's eye. Sold under their own names, these are legitimate. Upratna: traditional substitute stones lists them.
Mislabelled look-alikes. The same substitutes sold under the name of the principal stone: garnet as "ruby", citrine as "pukhraj", quartz cat's eye as "lehsunia". Cheap to detect — the refractive index and specific gravity do not match.
Synthetics sold as natural. Synthetic corundum in red, blue and yellow has been mass-produced for over a century and is the most common form of deception in the three sapphires. It is chemically the real thing, so only microscopic examination separates it.
Treated stones sold as untreated. Glass-filled ruby, heavily heated sapphire, resin-filled emerald, dyed coral and bleached or coated pearls. All natural, all altered, all requiring disclosure.
Manufactured imitations. Glass, plastic, reconstituted material. Sold mostly in the lowest price tier and at tourist locations.
What a laboratory test confirms — stone by stone
Ruby. Species (corundum vs garnet, spinel, glass); natural vs synthetic (inclusions); treatment — heating and, critically, glass filling, which can reduce a stone's real value by an order of magnitude. Ruby (Manik) identification guide.
Blue sapphire. Species; natural vs synthetic; heat treatment; diffusion treatment, where colour is cooked into a thin surface layer and a repolish would remove it. Blue sapphire (Neelam).
Yellow sapphire. Species (against citrine, yellow topaz, glass, synthetic corundum); heating; beryllium diffusion, which produces vivid yellow in pale material and needs advanced instruments to confirm. Yellow sapphire (Pukhraj).
Emerald. Species (against green glass, dyed quartz, synthetic beryl); natural vs synthetic; fracture filling with oil or resin, which nearly all emeralds have to some degree and which must be disclosed with its extent. Emerald (Panna).
Pearl. Natural vs cultured — an X-ray question, since a cultured pearl has a bead nucleus or a tissue centre that a natural pearl lacks; imitation (coated glass or plastic); treatments such as bleaching, dyeing and coating. Pearl (Moti): natural, cultured and imitation.
Red coral. Genuine Corallium coral vs dyed white coral, reconstituted coral powder, dyed bone or shell, plastic and glass. Structure under magnification and dye tests settle it. Red coral (Moonga).
Hessonite. Grossular garnet identified by RI and SG and by its characteristic "treacle" swirled inclusions; separated from spessartine garnet, orange zircon, glass and synthetic material. Hessonite (Gomed).
Cat's eye. Chrysoberyl cat's eye (RI about 1.74–1.75, SG about 3.7) vs quartz cat's eye (1.54, 2.65), apatite, tourmaline, and glass or fibre-optic imitations with an unnaturally sharp eye. Cat's eye (Lehsunia).
Diamond. Diamond vs moissanite, cubic zirconia, white sapphire and glass by thermal and electrical conductivity, RI and dispersion; natural vs laboratory-grown (HPHT and CVD), which needs specialised screening; treatments such as HPHT colour enhancement and fracture filling. Diamond (Heera): the basics.
Weight, ratti and what the report gives you
Astrological practice usually specifies a minimum weight in ratti. One ratti is conventionally taken as 0.1215 g (about 0.6 ct) in the modern standardised form, though older regional ratti varied. A laboratory reports weight in carats and grams, which convert unambiguously; a report giving only ratti, or no weight at all, is a warning sign. Ratti, carat and gram has the conversions.
What testing does not confirm
A laboratory can tell you that a stone is natural, untreated yellow sapphire of a stated weight. It cannot tell you that the stone is "suitable" for a particular person, that it has been "energised", or that it will have any effect. Those are matters of belief and practice, outside the scope of any test, and a certificate that makes such claims is telling you about the issuer rather than the stone.
Frequently asked questions
Which of the nine gems is most often faked?
By volume, ruby and the two sapphires, because synthetic corundum is cheap, abundant and chemically identical to the natural stone. Coral and pearl are the most frequently treated — dyed, bleached or reconstituted.
Does a substitute stone need to be tested?
If you are paying for a specific stone, yes: a "peridot" can be green glass and a "moonstone" can be opalescent plastic. The test is the same as for the principal gem — species, natural or synthetic, treatment.
Can one laboratory report cover a whole Navratna set?
Each stone is tested and described separately; a set may be reported on a single document listing all nine, or on nine reports. Either way each stone should have its own weight, measurements and findings.
Is a heated sapphire acceptable as a Navratna stone?
That is a question for the wearer's own tradition and adviser. The laboratory's role is to state clearly whether heating was detected so that the decision is informed.
Why does the same stone name have different prices?
Because the name alone does not say natural or synthetic, treated or untreated, or the quality grade. Two "blue sapphires" of the same weight can differ in price a hundredfold on those three questions.