Ruby Gemstone Guide: Colour, Quality, Origins and Value

What is a ruby gemstone?

A ruby is the red variety of the mineral corundum, which is crystallised aluminium oxide (Al₂O₃). Pure corundum is colourless. A trace of chromium, usually well under one per cent, replaces some of the aluminium and turns the crystal red. Every other colour of corundum is called sapphire, so ruby and sapphire are chemically the same gem. Ruby sits with emerald and sapphire at the top of the coloured gemstones overview.

Because it is corundum, a natural ruby shares sapphire's physical properties almost exactly. Those properties are what a gemmologist measures to identify it, and they are why ruby wears so well. Our full table of gemstone properties puts these numbers beside other stones.

Where does ruby stop and pink sapphire start? There is no single worldwide line. A stone is called ruby when red is clearly the dominant colour and it is saturated enough; paler or pinker stones are pink sapphire. Borderline stones can be called ruby by one laboratory and pink sapphire by another, which is worth knowing when you compare prices. Our guide on how ruby and sapphire compare in a ring covers the choice from the wearer's side.

Ruby is also the birthstone for July and the traditional gift for a 40th wedding anniversary.

What colour is the most valuable ruby?

Colour drives ruby value more than anything else. Gemmologists describe it in three parts: hue (the colour itself), tone (how light or dark) and saturation (how intense). The most sought-after rubies are a pure to slightly purplish red, medium to medium-dark in tone, with vivid saturation.

The trade term pigeon's blood ruby describes that top colour, usually with strong red fluorescence that makes the stone seem to glow from within. Some laboratories, such as SSEF and GRS, use it as a colour term on their reports, each with its own criteria. It is not a grade on a universal scale, so treat it as one lab's opinion rather than a fixed standard of quality.

• Too orange: reads warm and slightly brown in low light, and is valued less.
• Too purple or pink: moves towards pink sapphire territory.
• Too dark: iron-rich rubies can look almost black in the centre, especially in deep-cut stones.
• Fluorescence: low-iron rubies fluoresce strongly and look brighter in daylight; iron dampens this glow.

Ruby also shows two colours depending on the viewing direction, called dichroism. A good cutter orients the stone so the purer red shows through the table (the large top facet).

Where do rubies come from, and are there Australian rubies?

Origin affects both appearance and price, because rubies from different deposits tend to carry different amounts of iron and chromium. Origin can only be determined by a laboratory, and not every stone can be assigned one.

Australian ruby is a short story. Australia is famous for sapphire from the New England fields of NSW and the Anakie fields of central Queensland, but red corundum is rare here. Small quantities of ruby and pinkish red corundum have been found with sapphire in eastern Australian alluvial deposits, including the Barrington Tops area of NSW, yet there is no significant commercial ruby production. If a stone is sold as an Australian ruby, ask for laboratory documentation.

How is ruby quality judged?

There is no single grading scale for coloured stones like the D–Z scale for diamonds, so ruby quality is judged by eye against experience. The four factors, in order of importance:

• Colour: hue, tone and saturation, as above. It usually accounts for most of the value.
• Clarity: GIA classes ruby as a Type II gem, meaning small inclusions are expected. Fine needles of rutile, called silk, can soften light pleasantly; fractures near the surface are a durability concern.
• Cut: most rubies are mixed cuts (a brilliant-style crown over a step-cut pavilion) and are often cut deep to save weight. A window, a washed-out area in the centre, means light is passing straight through.
• Carat: fine rubies over 1 carat are uncommon and above 3 carats are rare, so price per carat rises sharply with size.

A 1 carat ruby is smaller face-up than a 1 carat diamond because corundum is denser (SG about 4.00 against 3.52). Our detailed guide on judging ruby colour, clarity and cut works through real examples.

Dense silk aligned in three directions can produce a six-rayed star when the stone is cut as a cabochon. These are covered in our guide to star rubies and star sapphires.

Are most rubies heat-treated?

Yes. Most rubies on the market have been heated to improve colour and clarity, and a heat-treated ruby is accepted across the trade as long as it is disclosed. Heating dissolves some silk and reduces purple or brown tones. Unheated rubies with fine colour are much rarer and sell for considerably more.

A composite ruby (sometimes sold as glass-filled) can contain a large share of glass by volume and is closer to a manufactured product than a natural ruby. It is inexpensive for a reason. A jeweller's torch during a repair can damage it, so always tell your jeweller what you have. See how to care for each gemstone for cleaning advice by treatment.

Is ruby hard enough for an engagement ring?

Yes. Ruby hardness is 9 on the Mohs scale, second only to diamond among popular gems, and its toughness (resistance to chipping and breaking) is rated excellent because corundum has no cleavage. Hardness and toughness are different things, as our guide to gemstone hardness explains.

Ruby will still scratch against diamond and can chip with a hard knock on an edge, so the setting matters. Claws over the corners, or a bezel for an active lifestyle, protect it. Ruby compared with diamond looks at how each wears over decades, ruby engagement ring designs shows styles, and our setting guide for diamonds and gemstones explains each setting type.

How to tell if a ruby is real?

Many red stones have been mistaken for ruby. The famous Black Prince's Ruby in the British Imperial State Crown is actually a red spinel. Today a gemmologist separates ruby from look-alikes with a few measured properties:

• Refractive index: ruby reads 1.762–1.770 and is doubly refractive. Red spinel is singly refractive at about 1.718; red garnets are singly refractive, roughly 1.74–1.81.
• Dichroscope: ruby shows two distinct reds. Spinel, garnet and glass show one.
• Inclusions under magnification: natural ruby shows straight, angular growth zoning, silk and mineral crystals. Flame-fusion lab-created ruby shows curved growth lines and round gas bubbles; flux-grown stones show wispy flux fingerprints and sometimes platinum platelets.
• Glass-filled stones: blue or orange flashes in fractures and trapped gas bubbles in the filler.
• Red tourmaline: lower RI (1.62–1.64) and much higher birefringence.

Our scientific guide to gemstone identification explains each instrument, and the jewellery and gem glossary defines terms such as birefringence and pleochroism.

Natural vs lab-created ruby: what is the difference?

A lab-created ruby (also called synthetic or laboratory-grown ruby) has the same chemistry, hardness and optical properties as a natural ruby. It is genuine corundum, grown in a laboratory rather than in the earth. Flame-fusion (Verneuil) ruby has been made since the early 1900s, and flux-grown and hydrothermal methods produce stones with more natural-looking inclusions.

Natural rubies are rare and many people value their geological origin; lab-created rubies give the same colour and durability for much less. Both are honest choices when disclosed. Read more in our guide to lab-grown sapphire, ruby and emerald and the wider overview of man-made gemstones.

How much does a ruby gemstone cost in Australia?

Ruby prices span a wider range than almost any other gem, because colour, treatment and origin each move the figure dramatically. These are approximate ranges for loose stones, in AUD, as a starting point only.

Expect price per carat to climb steeply past 1 and 2 carats. Origin reports naming Myanmar, and reports confirming no heat, add significantly. A ruby's resale value is not predictable, so choose it because you love the colour, not in the hope it will rise in value.

How to buy a ruby gemstone: step by step

1. Choose natural or lab-created first. This sets your budget range more than anything else.
2. Judge the colour in daylight and indoor light. Look for an even red without a dark centre, brown cast or washed-out window.
3. Ask about treatment. Heat-only is standard; heat with residue, diffusion and glass filling must be disclosed and change both price and care.
4. Ask for a report on significant stones. For rubies above about 1 carat or claimed as unheated, a report from a recognised lab such as GIA, SSEF, GRS or Gübelin confirms identity, treatment and sometimes origin.
5. Check for surface-reaching fractures. Under a loupe, these are the weak points in a ring stone.
6. Plan the setting and metal. Yellow and rose gold warm a ruby; white metals make it look cooler and redder. Think about protection for the corners or edges.
7. Compare it with alternatives. If you are still deciding, our guide to engagement rings with colour and meaning compares ruby with sapphire, emerald and spinel.

GemTrove has worked with coloured gemstones since it was founded in 2008, from a family jewellery trade that goes back to 1984. Raj Sood, a Graduate Gemologist (GIA), checks identity and treatment on every ruby we set.