Blue Sapphire vs. Blue Spinel: A Gemstone Comparison

Blue Sapphire and Blue Spinel are two gemstones that can easily be mistaken for each other. With their deep blue hues and strong brilliance, they often appear strikingly similar, especially when seen in jewellery.

Historically, Spinel has even been misidentified as Sapphire in royal jewels! Despite their resemblance, these two gemstones differ in composition, rarity, and value, making it essential to understand their unique traits before making a purchase.

The confusion between Blue Sapphire and Blue Spinel is partly due to their overlapping sources and the fact that natural Blue Spinel is much rarer than Sapphire, yet often less expensive. Additionally, many people are more familiar with Sapphire, so Spinel is sometimes overlooked, even though it has exceptional qualities of its own.

So, how do you tell them apart? Whether you’re a jeweller sourcing gemstones or a collector seeking the perfect blue stone, knowing their differences can help you make an informed decision.

Let’s break down the key distinctions between Blue Sapphire and Blue Spinel, from their gemmological properties to their symbolism.

How to Tell the Difference: Visual & Gemmological Tests

Visual Clues

• Blue Sapphire: Rich, deep blue with strong colour saturation. May have a slight violet or greenish undertone, depending on the origin.
  
  
• Blue Spinel: Slightly lighter and more ‘steely’ blue, often appearing purer in tone with no colour zoning.

Gemmological Tests

I've included the table below to compare the results of a few commonly done tests, but the most striking difference between the 2 is that Spinel is one of the rare gemstones that is singly refractive, meaning light doesn't split when it enters them. 

Test	Blue Sapphire	Blue Spinel
Refractive Index (RI)	1.760–1.778	1.718–1.735
Birefringence	0.008–0.010	None (singly refractive)
Pleochroism	Two colours (blue, violet/green)	None
UV Fluorescence	Weak to strong (in some varieties)	Often strong red under longwave UV
Optical Character	Doubly refractive, uniaxial negative	Singly refractive (can show anomalous double refraction)

Colour

• Blue Sapphire: Deep, rich blue with a velvety appearance. Colour zoning is common in natural stones.
  
  
• Blue Spinel: Typically a lighter, steelier (slightly grey) blue. It has a uniform colour as it doesn't exhibit colour zoning like Sapphire does.

Clarity & Inclusions

• Blue Sapphire: Type 2 gemstone, meaning it's usually included. Sapphires often contain needle-like rutile inclusions known as silk (due to the thread-like appearance and pattern, making them look like a sheet of silk when viewed with strong enough magnification). High-quality stones have minimal visible inclusions.
  
  
• Blue Spinel: Also a type 2 gemstone, though it's generally less included than Sapphire. It's very rare for Spinel to have silk inclusions.

Gemstone Formation

• Blue Sapphire: A variety of corundum, formed in metamorphic or igneous environments. Colour is caused by iron and titanium.
  
  
• Blue Spinel: A magnesium aluminium oxide mineral that forms in marble and alluvial deposits. Colour comes from trace elements like iron or cobalt.

Durability & Wearability

Scratch Resistance (Mohs Hardness Scale):

• Blue Sapphire: 9 (very durable, excellent for everyday wear)
  
  
• Blue Spinel: 7.5–8 (very good, but slightly more prone to scratches than Sapphire)

Cleavage & Toughness:

• Blue Sapphire: No cleavage, excellent toughness.
  
  
• Blue Spinel: No cleavage, very good toughness.

Best Use
While both stones are excellent for any type of jewellery, Sapphire is slightly more durable for rings that will be worn all the time.

Enhancements & Treatments

• Blue Sapphire: Commonly heat-treated to improve colour and clarity. Some stones undergo a chemical treatment called diffusion which changes the colour of the gemstone by introducing trace elements into it. This treatment doesn't go all the way through the gem so it can be detected via an immersion test.
  
  
• Blue Spinel: Rarely undergoes any treatments.

Both Sapphire and Spinel can be synthesised, so it's quiet common to find lab-grown versions of these gems on the market.

Price Comparison

• Blue Sapphire: Prices vary greatly based on colour, natural clarity and origin. High-quality Sapphires range from £100–£5,000+ per carat, with premium Kashmir and Burmese stones commanding even higher prices.
  
  
• Blue Spinel: More affordable, with prices ranging from £100–£1,000 per carat, though rare cobalt blue Spinel can be significantly more expensive.

Size Availability

• Blue Sapphire: Most faceted blue sapphires fall between 0.50 to 5 carats.
  
  
• Blue Spinel: Tend to be smaller with most faceted blue spinels fall between 0.50 to 3 carats.

Rarity & Sourcing

• Blue Sapphire: A relatively common gemstone that's found in Sri Lanka, Myanmar, Madagascar, Australia, and Thailand.
  
  
• Blue Spinel: Rare in gem-quality blues, sourced from Myanmar, Sri Lanka, Vietnam, and Tanzania.

Cut & Shape Preferences

• Blue Sapphire: Often cut into ovals, cushions, and rounds to maximise colour and brilliance.
  
  
• Blue Spinel: Commonly cut into cushions and rounds, though it often has a slightly lower refractive index, meaning it may not sparkle as much as Sapphire.

Symbolic & Spiritual Associations

• Blue Sapphire: Linked to wisdom, loyalty, and divine favour.
  
  
• Blue Spinel: Associated with rejuvenation, inspiration, and energy.

Comparison Summary

Feature	Blue Sapphire	Blue Spinel
Hardness	9	7.5–8
Cleavage	None	None
Colour	Deep blue, may have zoning	Steely blue, pure tone
Commonly Included?	Type 2 - Usually included (silk, colour zoning)	Type 2 - Usually less included than sapphire
Common Treatments	Heat, diffusion	Rarely treated
Price per Carat	£100–£5,000+	£100–£1,000
Rarity	Available, but top-quality is rare	Rare in high-quality blues
Large Sizes? (5 ct+)	Available but expensive	Very Rare, but more affordable than Sapphire
Associated With	Wisdom, loyalty	Rejuvenation, energy

Blue Sapphire and Blue Spinel may appear similar, but their differences in composition, price, and rarity make them distinct choices for jewellers and collectors.

If you’re looking for a classic, time-honoured gemstone with strong durability, Blue Sapphire is a fantastic choice. However, if you prefer a rarer, naturally vibrant gemstone that is often untreated and more affordable, Blue Spinel is an excellent alternative. Either way, both gemstones offer stunning blue hues that make any jewellery piece shine!