How to Tell Cubic Zirconia from a Diamond: A Comprehensive Guide

Diamonds, renowned for their brilliance, fire, and exceptional hardness, have captivated humanity for centuries. However, their high value has led to the creation of numerous imitations, with cubic zirconia (CZ) being one of the most common. While CZ can closely resemble a diamond to the untrained eye, several key differences allow for relatively easy differentiation. This comprehensive guide will provide you with detailed steps and instructions to confidently distinguish between a cubic zirconia and a genuine diamond.

Understanding Diamonds and Cubic Zirconia

Before diving into the identification methods, it’s crucial to understand the fundamental properties of both diamonds and cubic zirconia.

Diamonds: Nature’s Masterpiece

• Composition: Diamonds are composed of pure carbon atoms arranged in a specific crystal structure.
• Hardness: Diamonds are the hardest naturally occurring substance, scoring a perfect 10 on the Mohs hardness scale. This extreme hardness makes them incredibly resistant to scratching.
• Brilliance: Brilliance refers to the amount of light reflected from the diamond back to the observer’s eye. Diamonds have a high refractive index, meaning they bend light significantly, contributing to their exceptional brilliance.
• Fire (Dispersion): Fire is the term used to describe the colorful flashes of light emitted by a diamond, often referred to as its “sparkle.” Diamonds exhibit a high level of dispersion, creating vibrant spectral colors.
• Clarity: Clarity refers to the absence of inclusions (internal flaws) and blemishes (external flaws) in a diamond.
• Rarity: Natural diamonds are rare, formed deep within the Earth over billions of years under immense pressure and heat.

Cubic Zirconia: A Synthetic Simulant

• Composition: Cubic zirconia is a synthetic (man-made) material composed of zirconium dioxide (ZrO2).
• Hardness: CZ has a hardness of around 8.5 on the Mohs scale, making it durable but significantly softer than a diamond.
• Brilliance: While CZ can be cut to achieve a high level of brilliance, it generally does not reflect light as effectively as a diamond.
• Fire (Dispersion): CZ exhibits more fire than a diamond, producing a greater amount of colorful flashes. However, the colors tend to be more artificial-looking and less refined.
• Clarity: CZ is typically flawless, lacking the natural inclusions that are often present in diamonds.
• Abundance: CZ is readily available and relatively inexpensive to produce.

Methods for Distinguishing Cubic Zirconia from a Diamond

Now, let’s explore various methods you can use to differentiate between CZ and a diamond:

1. The Water Test

Principle: Diamonds are denser than cubic zirconia. This means that a diamond will sink faster in water than a CZ stone of comparable size.

Procedure:

1. Fill a glass with water.
2. Carefully drop the stone into the glass.
3. Observe its behavior.

Results:

• Diamond: A diamond will sink quickly to the bottom.
• Cubic Zirconia: A CZ will sink more slowly or may even float momentarily before sinking.

Limitations: This test is not foolproof, as very small differences in sinking speed can be difficult to perceive. It’s more reliable with larger stones.

2. The Newspaper Test (Read-Through Test)

Principle: A diamond’s refractive properties bend light in a way that prevents you from clearly seeing through it. A CZ, on the other hand, allows light to pass through more directly.

Procedure:

1. Place a newspaper or any printed material with text on a flat surface.
2. Position the stone table-down (the large, flat facet on top) on the text.
3. Observe the text through the stone.

Results:

• Diamond: You will not be able to clearly read the text through the diamond. The text will appear heavily distorted or blurred.
• Cubic Zirconia: You will likely be able to see the text through the CZ, although it may be slightly blurred.

Limitations: This test works best with loose stones. If the stone is mounted, it may be difficult to perform the test accurately. Also, very well-cut diamonds with specific facet arrangements may allow some distorted visibility, though not as clear as with a CZ.

3. The Fog Test (Breath Test)

Principle: Diamonds disperse heat rapidly, while CZ retains heat for a longer period. This difference in thermal conductivity can be observed by breathing on the stone.

Procedure:

1. Hold the stone a few inches from your mouth.
2. Breathe on the stone, creating a fog on its surface (similar to fogging a mirror).
3. Observe how quickly the fog dissipates.

Results:

• Diamond: The fog will dissipate almost immediately (within 1-2 seconds).
• Cubic Zirconia: The fog will linger for a longer period (3-5 seconds or more).

Limitations: This test can be affected by the surrounding temperature and humidity. It’s also important to ensure that both stones are clean before performing the test. Comparing two stones side-by-side will yield the best results.

4. The Hardness Test (Scratch Test) – Use with Caution!

Principle: Diamonds are the hardest naturally occurring substance. They can only be scratched by another diamond.

Procedure: This test is highly discouraged for valuable or sentimental stones, as it can potentially damage the stone if you are unsure of its composition. If you choose to proceed, use extreme caution.

1. Ideally, use a known piece of corundum (hardness of 9 on the Mohs scale) or a diamond testing pen.
2. Gently attempt to scratch the surface of the stone with the corundum or the testing pen.

Results:

• Diamond: A diamond will not be scratched by corundum. A diamond testing pen will usually give a positive reading (depending on the type of pen used).
• Cubic Zirconia: A CZ will likely be scratched by corundum. Diamond testing pens may give mixed results.

Important Considerations:

• Risk of Damage: This test carries a significant risk of damaging the stone, especially if you are not experienced.
• Ethical Concerns: It is generally not acceptable to scratch someone else’s jewelry without their permission.
• Diamond Simulants: Some other diamond simulants are also very hard and may not scratch easily.

We strongly recommend avoiding this test unless you are a trained gemologist and have the appropriate tools and expertise.

5. The Brilliance and Fire Observation

Principle: Diamonds and CZ exhibit differences in their brilliance and fire.

Procedure:

1. Examine the stone under bright, direct light (ideally natural sunlight).
2. Observe the way the stone reflects light and the colors it produces.

Results:

• Diamond: A diamond will display a bright, white brilliance with flashes of spectral colors (fire). The sparkle will be more subtle and refined.
• Cubic Zirconia: A CZ will exhibit a more intense and colorful sparkle. The fire may appear more artificial and less nuanced. CZ often has an almost rainbow-like effect, with very strong orange flashes.

Key Differences to Look For:

• Brilliance Color: Diamond brilliance is generally white or near-white. CZ can have a slightly yellow or grayish tint.
• Fire Intensity: CZ displays more fire than a diamond.
• Sparkle Quality: Diamond sparkle is more refined and subtle, while CZ sparkle is often described as “splintery” or overly flashy.

6. The Weight Test

Principle: Cubic zirconia is significantly heavier than a diamond of the same size and shape.

Procedure:

1. Use a jeweler’s scale to weigh the stone.
2. Compare the weight to the expected weight of a diamond of similar dimensions.

Results:

• Diamond: The weight will be consistent with the expected weight for a diamond of its size. You’ll need a diamond weight chart for comparison.
• Cubic Zirconia: The weight will be noticeably higher than the expected weight for a diamond of the same size.

Limitations: This test requires specialized equipment and knowledge of diamond weights. It’s most useful for gemologists or jewelers.

7. The Ultraviolet (UV) Light Test

Principle: Some diamonds fluoresce under ultraviolet (UV) light, while CZ generally does not.

Procedure:

1. Place the stone under a UV light source (such as a black light).
2. Observe its reaction.

Results:

• Diamond: Some diamonds will exhibit a blue fluorescence under UV light. The intensity of the fluorescence can vary from strong to weak. However, some diamonds do not fluoresce at all.
• Cubic Zirconia: CZ typically does not fluoresce under UV light. It may show a very faint yellow or greenish glow, but this is rare.

Limitations: This test is not conclusive, as not all diamonds fluoresce. Also, some treated CZ stones may exhibit fluorescence. It’s best used in conjunction with other tests.

8. Examine the Setting and Mount

Principle: Genuine diamonds are usually set in high-quality metals like gold, platinum, or silver. CZ stones are often set in less expensive metals.

Procedure:

1. Carefully examine the setting and mount of the stone.
2. Look for hallmarks or stamps that indicate the metal type (e.g., 14K, 18K, Pt950, Sterling Silver).

Results:

• Diamond: A diamond is likely to be set in a precious metal.
• Cubic Zirconia: A CZ may be set in a base metal or a lower-quality alloy.

Important Note: This is not a definitive test, as some CZ stones may be set in high-quality metals, especially in custom-made jewelry.

9. The Loupe Examination

Principle: A jeweler’s loupe (a magnifying glass specifically designed for examining gemstones) can reveal subtle differences in the surface and internal characteristics of diamonds and CZ.

Procedure:

1. Use a 10x or higher magnification jeweler’s loupe.
2. Carefully examine the stone’s facets, edges, and internal structure.

Results:

• Diamond: A diamond may exhibit small inclusions (internal flaws) or blemishes (surface imperfections). The facet junctions will be sharp and well-defined.
• Cubic Zirconia: CZ is typically flawless. You will likely not see any inclusions or blemishes. The facet junctions may be slightly rounded or less sharp than those of a diamond. CZ can also show very fine polishing marks under magnification.

Limitations: This test requires experience and a trained eye to interpret the observations accurately.

10. Professional Appraisal

The most reliable way to determine whether a stone is a diamond or a CZ is to have it professionally appraised by a qualified gemologist.

Procedure:

1. Take the stone to a certified gemologist or appraiser.
2. Request a written appraisal that identifies the stone and provides its characteristics.

Benefits of Professional Appraisal:

• Expertise: Gemologists have the knowledge, experience, and equipment to accurately identify and evaluate gemstones.
• Objectivity: A professional appraisal provides an unbiased assessment of the stone’s value.
• Documentation: A written appraisal serves as proof of the stone’s identity and value, which can be useful for insurance purposes.

Summary Table of Key Differences

Here’s a quick reference table summarizing the key differences between diamonds and cubic zirconia:

Conclusion

While cubic zirconia can be a beautiful and affordable alternative to diamonds, it’s essential to be able to distinguish between the two. By using the methods outlined in this guide, you can confidently assess the characteristics of a stone and make an informed decision. Remember to exercise caution when performing tests that could potentially damage the stone, and when in doubt, seek the expertise of a qualified gemologist.

Understanding the properties of both diamonds and cubic zirconia, combined with careful observation and testing, will empower you to identify these gemstones with greater accuracy and appreciation.