Types of gemstones: sapphire, topaz, opal, coral and how to tell them apart

Walk into any gemstone shop in India and you will hear the same names: pukhraj, neelam, panna, manik, moonga, moti. Behind each name sits a specific mineral (or, in the case of coral and pearl, an organic material) with its own colour, hardness and tell-tale signs. This guide explains the main types of gemstones we sell, how they differ, and the simple checks that separate a natural stone from glass, synthetic or a dyed substitute.

If you are buying a stone for astrological wear rather than for jewellery, read this alongside our guide to gemstones in Vedic astrology.

First, a quick word on hardness

Gemmologists rate scratch resistance on the Mohs scale from 1 (talc) to 10 (diamond). It is the single most useful number to remember, because most imitations are softer than the stone they copy. Glass sits at about 5.5, quartz at 7, topaz at 8, sapphire and ruby at 9. A real sapphire will scratch glass easily; a piece of blue glass sold as sapphire will not scratch a quartz crystal. We do not recommend scratch testing a cut stone yourself (it can damage the facet edges), but knowing the numbers helps you ask the right questions.

Sapphires: neelam and pukhraj

Blue sapphire (neelam) and yellow sapphire (pukhraj) are the same mineral, corundum, in different colours. Ruby (manik) is red corundum. All three sit at 9 on the Mohs scale, which is why they take such a bright polish and hold it for decades.

How a natural sapphire looks

• Colour zoning: natural sapphires often show slightly uneven bands of colour when viewed against white paper. Perfectly even colour throughout is more typical of synthetic corundum.
• Silk: fine needle-like inclusions (rutile) that catch the light. A stone with some silk is almost certainly natural.
• Lustre: a hard, glassy shine on the facets. Glass imitations look softer and their facet edges wear round with time.

What it is confused with

Neelam is often confused with blue topaz, iolite, tanzanite and blue glass. Pukhraj is confused with citrine (yellow quartz) and yellow topaz. The giveaways: topaz and citrine are lighter in the hand for their size, have a less intense lustre, and glass often contains round gas bubbles visible under a 10x loupe. Origin matters for price: Sri Lankan (Ceylon) sapphires are prized for their clarity, while Bangkok-cut stones are the affordable entry point. Both are listed as separate grades on our product pages, with the starting rate per carat.

Topaz: white and blue

Topaz is an aluminium silicate with a Mohs hardness of 8. It is a genuine natural gemstone, but it is also the most common stand-in for costlier stones, so it helps to know it well.

• White topaz is colourless and is widely worn as an affordable substitute for diamond (hira). Compared with diamond it has less fire (the rainbow flashes) and a lower refractive index, so it looks quieter and more glassy. It is far more brilliant than quartz, though, and much cheaper than diamond.
• Blue topaz is a clear, even sky-blue to Swiss-blue. Almost all blue topaz in the market gets its colour through treatment of naturally colourless topaz; ask any seller to state the treatment. It is a popular substitute for neelam.

Topaz has perfect cleavage in one direction, meaning a sharp knock can split it along a flat plane. Set it in a protective bezel and avoid ultrasonic cleaners.

Opals: Ethiopian and Australian

Opal is hydrated silica, not a crystal at all, which is why it shows play of colour: flashes of green, orange, blue and red that move as you tilt the stone. It is soft (5.5 to 6.5) and contains water, so it needs gentle handling.

• Australian opal is the classic, stable variety. The colour play sits within a milky or dark body and does not change when the stone gets wet.
• Ethiopian opal (Welo) is hydrophane: it absorbs water and can turn temporarily transparent when soaked, then returns to normal as it dries. It usually shows brighter, more crystal-like colour play at a lower price.

Spotting imitation opal

Synthetic opal shows a very regular "chicken wire" or columnar pattern when viewed from the side. Doublets and triplets (a thin slice of real opal glued to a dark backing) show a perfectly straight glue line at the girdle. Natural opal has irregular, cloud-like colour patches. Compare the two grades on our opal stone page.

Coral: moonga

Red coral (moonga) is organic, formed by marine polyps, and is one of the softest stones worn in India at 3 to 4 on the Mohs scale. It is cut into cabochons rather than faceted, most commonly in triangle, capsule and oval shapes.

How to check natural coral

• Grain: under a loupe, natural coral shows fine parallel lines or a wood-grain texture. Dyed plastic or reconstituted coral looks uniform.
• Colour: real moonga ranges from salmon to deep ox-blood red, usually with slight variation across the piece. Dead-flat, perfectly even red is a warning sign.
• Weight and temperature: coral feels dense and cool; plastic imitations feel light and warm up quickly in the hand.
• Acid reaction: a jeweller can confirm coral with a tiny drop of acid on an unseen edge (it fizzes, because coral is calcium carbonate). Never do this yourself.

Coral is porous. Keep it away from perfume, sweat and household chemicals, and wipe it with a soft cloth after wear.

Other natural stones worth knowing

Emerald (panna)

Green beryl, Mohs 7.5 to 8. Nearly every natural emerald contains visible inclusions (the "jardin"), and a flawless, glass-clear green stone at a low price is almost certainly synthetic or glass. Zambian emeralds tend to be bluish-green and cleaner; Colombian stones are the warm, grassy green that commands the highest prices.

Pearl (moti)

An organic gem from oysters and mussels. Natural and cultured pearls feel slightly gritty when rubbed gently against a tooth; glass and plastic imitations feel smooth. Look for a soft, layered lustre and small surface irregularities, both signs of a real pearl. South Sea pearls are larger with a satin sheen; Venezuelan and Basra pearls are natural (not cultured) and priced far higher.

Cat's eye (lehsunia)

Chrysoberyl cat's eye shows a single sharp band of light that glides across the dome as you turn it, an effect called chatoyancy. A real lehsunia has a crisp, narrow "eye" that opens and closes under a single light source. Quartz cat's eye and fibre-optic glass show a broader, fuzzier band.

Hessonite (gomed)

A honey to cinnamon-brown garnet. Natural gomed has a characteristic "heat wave" or treacle-like roiled look inside when viewed with a loupe, which is very hard to fake in glass.

Moonstone, peridot, amethyst and turquoise

• Moonstone: a feldspar with a floating blue or white sheen (adularescence) that seems to sit below the surface. Imitations in glass have a flat, surface-level shimmer.
• Peridot: olive to lime green olivine. It is one of the few gems found in only one colour, so any "peridot" that is blue or yellow is not peridot.
• Amethyst (jamunia): violet quartz, Mohs 7. Natural stones usually show colour zoning and are cooler in tone than the very even, deep purple of synthetic quartz.
• Turquoise (firoza): opaque sky-blue to green with a matrix of brown or black veins. Reconstituted or dyed howlite has veins that sit on the surface and colour that rubs off on a damp cloth. Iranian (Irani) firoza is the traditional benchmark.

A simple buying checklist

1. Ask for a lab certificate. Every loose gemstone we sell can ship with a GTL laboratory report that states the species, natural or synthetic, and any treatment.
2. Look inside, not just at the surface. A 10x loupe costs very little. Natural stones have natural inclusions; glass has bubbles and swirl marks.
3. Weigh it against the price. A stone priced far below the going rate per carat for its origin and grade is usually not what it claims to be.
4. Check the treatment line. Heating, dyeing and glass filling are common in the trade. They should be disclosed on the certificate and on the product page.
5. Buy loose, then set. A loose stone can be examined from every side; a set stone hides the pavilion and the girdle.

Browse our full range of certified loose gemstones, priced per carat with the origin, treatment and certificate stated on every page, or explore gemstones and crystals for bracelets, idols and sphatik.

Frequently asked questions

Is blue topaz the same as blue sapphire?

No. Sapphire is corundum (Mohs 9); topaz is a softer, lighter silicate (Mohs 8). Blue topaz is widely worn as an affordable substitute for neelam, but they are different minerals with very different prices.

Can I test a gemstone at home?

You can do a lot with a loupe and good light: look for bubbles (glass), perfectly even colour (synthetic), and a glue line at the girdle (doublet). For a definitive answer, a laboratory report is the only reliable proof.

What does "per carat" pricing mean?

One carat is 0.2 grams. Loose gemstones are priced by weight and quality, so the listed price is the starting rate for one carat of the stated grade; the final price depends on the exact stone you choose. We share photos and the certificate before billing.

Descriptions of traditional or spiritual use reflect Vedic belief and are not medical or professional advice.