Heated vs. Unheated Gemstones: Why it Matters?
In the world of fine gemstones, nothing sparks more conversation — or collector interest — than the difference between heated and unheated gemstones. As buyers become more educated and demand for untreated gems grows, understanding this distinction has never been more important.
“Unheated gemstones are gaining real momentum with collectors,” says jeweller Matthew Ely. “There’s a certain allure to a gem that’s come straight from the earth — untouched by human intervention.
What’s the Difference Between Heated and Unheated Gemstones?
At its simplest, heated gemstones are natural stones that have been subjected to high temperatures after mining to enhance their colour or clarity.
Unheated gemstones, by contrast, are left entirely untreated — showcasing their natural colour as formed by nature.
What’s the Difference Between Heated and Unheated Gemstones?
In the world of fine gemstones, nothing sparks more conversation — or collector interest — than the difference between heated and unheated gemstones. As buyers become more educated and demand for untreated gems grows, understanding this distinction has never been more important.
“Unheated gemstones are gaining real momentum with collectors,” says Matthew Ely. “There’s a certain allure to a gem
that’s come straight from the earth — untouched by human intervention.”
Why Are Some Gemstones Heated?
Heating has been used for centuries to improve the appearance of gems like sapphires, emeralds and rubies. Heat can deepen colour, dissolve inclusions, and enhance clarity.
For Sapphires: Heating can intensify blue hues or create uniformity in colour.
For Rubies: Heat treatment improves transparency and brightens the red.
For Other Gems: Some tourmalines, aquamarines, and morganites are also routinely heated.
“Heat treatment mimics what could happen naturally if the stone stayed underground under more pressure and heat,” explains Matthew.
“It’s a continuation of nature’s work — but it’s still human intervention.
Why Are Some Gemstones Heated?
Heating has been used for centuries to improve the appearance of gems like sapphires and rubies. Heat can deepen colour, dissolve inclusions, and enhance clarity.
For Sapphires: Heating can intensify blue hues or create uniformity in colour.
For Rubies: Heat treatment improves transparency and brightens the red.
For Other Gems: Some tourmalines, aquamarines, and zircons are also routinely heated.
“Heat treatment mimics what could happen naturally if the stone stayed underground under more pressure and heat,” explains Matthew.
“It’s a continuation of nature’s work — but it’s still human intervention.
Why Are Unheated Gemstones More Valuable?
Rarity: Only a small percentage of gemstones are naturally beautiful enough to remain unheated.
Collector Appeal: In a market that values authenticity, unheated gems have become highly desirable.
Transparency: Buyers appreciate knowing exactly what they’re getting — with no enhancements.
Certification Matters: Reputable gem labs like GIA and Lotus issue reports confirming unheated status, which significantly impacts value.
“Having that ‘unheated’ note on a certificate often increases a gem’s value — even if it means accepting some natural inclusions or softer colour,” says Matthew.
Why Are Unheated Gemstones More Valuable?
Rarity: Only a small percentage of gemstones are naturally beautiful enough to remain unheated.
Collector Appeal: In a market that values authenticity, unheated gems have become highly desirable.
Transparency: Buyers appreciate knowing exactly what they’re getting — with no enhancements.
Certification Matters: Reputable gem labs like GIA and Lotus issue reports confirming unheated status, which significantly impacts value.
“Having that ‘unheated’ note on a certificate often increases a gem’s value — even if it means accepting some natural inclusions or softer colour,” says Matthew.
How Can You Tell if a Gemstone is Heated or Unheated?
It takes a trained eye — and often a laboratory.
For example, in sapphires, heating changes how inclusions look under magnification.
Unheated sapphire: Needle-like inclusions appear whole and intact.
Heated sapphire: Those needles may break into smaller dots, showing signs of heat exposure.
However, low-temperature heat treatments are getting harder to detect, making certification even more important.
“If you’re investing in fine gemstones, certification is paramount,” says Matthew. “We’ll never label a stone as unheated unless we’re certain — and that usually means a lab report.”
How Can You Tell if a Gemstone is Heated or Unheated?
It takes a trained eye — and often a laboratory.
For example, in sapphires, heating changes how inclusions look under magnification:
Unheated sapphire: Needle-like inclusions appear whole and intact.
Heated sapphire: Those needles may break into smaller dots, showing signs of heat exposure.
However, low-temperature heat treatments are getting harder to detect, making certification even more important.
“If you’re investing in fine gemstones, certification is paramount,” says Matthew. “We’ll never label a stone as unheated unless we’re certain — and that usually means a lab report.”
Are Heated Gemstones Bad?
Not at all. Heat treatment is widely accepted in the gem trade — especially for jewellery-grade stones where appearance matters more than collectability.
“If you’re buying a beautiful sapphire or ruby for personal wear, a heated gem is totally fine,” Matthew says.
“We sell both. It depends on whether you want a gorgeous piece for yourself or a future investment.”
Are Heated Gemstones Bad?
Not at all. Heat treatment is widely accepted in the gem trade — especially for jewellery-grade stones where appearance matters more than collectability.
“If you’re buying a beautiful sapphire or ruby for personal wear, a heated gem is totally fine,” Matthew says.
“We sell both. It depends on whether you want a gorgeous piece for yourself or a future investment.”
Which Collector Gems Are Gaining Value for Being Unheated?
Spinel: Almost always unheated — and finally getting the recognition it deserves. Vibrant reds, hot pinks, and cobalt blues are particularly sought-after.
Garnet (Tsavorite & Spessartine): Naturally vivid and untreated. These colourful garnets are gaining serious traction with collectors.
Paraiba Tourmaline: Heat treatment is possible but rare — copper content gives its neon glow naturally. Certified copper-bearing stones are highly collectible.
Ruby & Sapphire: Unheated stones from renowned origins (like Burma for ruby or Kashmir for sapphire) fetch significant premiums.
“You can’t go wrong buying unheated stones from respected localities,” says Matthew. “Especially when combined with great colour and cutting.”
Which Collector Gems Are Gaining Value for Being Unheated?
Spinel: Almost always unheated — and finally getting the recognition it deserves. Vibrant reds, hot pinks, and cobalt blues are particularly sought-after.
Garnet (Tsavorite & Spessartine): Naturally vivid and untreated. These colourful garnets are gaining serious traction with collectors.
Paraiba Tourmaline: Heat treatment is possible but rare — copper content gives its neon glow naturally. Certified copper-bearing stones are highly collectible.
Ruby & Sapphire: Unheated stones from renowned origins (like Burma for ruby or Kashmir for sapphire) fetch significant premiums.
“You can’t go wrong buying unheated stones from respected localities,” says Matthew. “Especially when combined with great colour and cutting.”
Matthew Ely’s Buying Tips for Heated vs. Unheated Gems
Know Your Purpose: If you want a stunning piece for daily wear, a heated gem is perfectly fine. If you’re investing or collecting, prioritise unheated stones with certification.
Work with Trusted Jewellers: Transparency about treatment is crucial — always ask.
Consider Cut and Colour: Even unheated stones need strong colour and good cutting to hold value.
Certification is Key: Especially for higher-value purchases or investment pieces.
Matthew Ely’s Buying Tips for Heated vs. Unheated Gems
Know Your Purpose: If you want a stunning piece for daily wear, a heated gem is perfectly fine. If you’re investing or collecting, prioritise unheated stones with certification.
Work with Trusted Jewellers: Transparency about treatment is crucial — always ask.
Consider Cut and Colour: Even unheated stones need strong colour and good cutting to hold value.
Certification is Key: Especially for higher-value purchases or investment pieces.
