Introduction
Zircon and cubic zirconia (CZ) might look alike and have similar names but are completely different. Their chemistry and crystal structure are not the same. Here are some key facts about these two gemstones to clear up the confusion.
Both zircon and cubic zirconia are stunning, come in many colors, and are often used as diamond substitutes. However, despite their similar names, these stones are very different. Let's explore how they compare to diamonds and how you can tell them apart.
What Is Zircon?
Zircon is one of the oldest gemstones on Earth, even older than diamonds. A zircon crystal found in Jack Hills, Australia, is estimated to be 4.375 billion years old. Ancient civilizations have used zircon, which is even mentioned in the Bible, including in Exodus, as one of the gems in Aaron's breastplate.
Zircon is a natural mineral made mostly of zirconium oxide (ZrO4), with small amounts of other elements like hafnium (1% to 4%) mixed in. It also contains tiny amounts of radioactive elements like uranium and thorium. Zircon has many natural colors, including colorless, brown, blue, red, pink, yellow, green, purple, and gray. When brown zircon is heated, it can change to blue or become colorless.
Zircon's hardness is 6.5 to 7.5 on the Mohs scale, similar to that of materials like unglazed porcelain or amethyst. Its sparkle and fire make colorless zircon a popular diamond substitute. Zircon is also a December birthstone. Some types of zircon even have a unique cat' s-eye effect and come in a variety of colors.
What Is Cubic Zirconia?
Cubic Zirconia (CZ) is a man-made gemstone that mimics natural cubic zirconia's physical and optical properties. Natural cubic zirconia was first discovered in the 1930s as tiny inclusions in zircon crystals, but these natural crystals were too small to be used in jewelry. Today, no natural cubic zirconia is available on the market.
In the 1970s, scientists developed a way to create CZ in a lab, making it an affordable and popular diamond substitute. Lab-grown CZ is usually flawless, though it may sometimes have small gas bubbles or traces of zirconium oxide from the production process. CZ is quite hard, with a Mohs hardness of 8.5, which is similar to a masonry drill bit and harder than Topaz. Its shine is similar to a diamond, and it can be made in many colors by adding specific elements, allowing for options like synthetic sapphires, rubies, and other colored stones.
Cubic zirconia has a chemical formula of ZrO2, with a crystal structure and density that are different from zircon. Unlike zircon, CZ is pure and not radioactive. In its natural state, it is colorless, but added elements can create a wide range of vibrant colors.
Zircon vs Cubic Zirconia
Zircon and cubic zirconia contain zirconium, but their chemical makeup and crystal structures differ. They also differ in how they are made. Zircon is a natural mineral found in nature, while cubic zirconia is made in a lab. However, lab-made zircon and natural cubic zirconia also exist, though they are less common.
Both zircon and cubic zirconia come in many colors, including colorless options. One key difference in appearance is how they reflect light: zircon has less "fire" (the colorful flashes of light) compared to a diamond, while cubic zirconia has more fire.
Since zircon is a natural stone, it often contains tiny amounts of other elements like uranium and thorium, which make it slightly radioactive. On the other hand, cubic zirconia is pure and not radioactive. Both gemstones are good at insulating against heat.
| Property | Zircon | Cubic Zirconia |
|---|---|---|
| Chemical Formula | ZrO4 | ZrO2 |
| Occurrence | Natural | Synthetic |
| Crystal Structure | Tetragonal | Cubic |
| Mohs Hardness | 7.5 | 8.0-8.5 |
| Specific Gravity | 4.6-4.7 g/cm3 | 5.6-6.0 g/cm3 |
| Refractive Index | 1.92-1.96 | 2.15-2.18 |
| Dispersion | 0.039 (less than diamond) | 0.058-0.066 (more than diamond) |
| Birefringence | 0.047–0.055 | none |
| Radioactive | yes | no |
| Fracture | Conchoidal | Conchoidal |
| Color | various | various |
| Fluorescence | yes | yes |
How to Tell Zircon and Cubic Zirconia Apart
Zircon and cubic zirconia are both beautiful, durable, and affordable alternatives to diamonds, but there are some clear ways to tell them apart:
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Radioactivity: Zircon can be slightly radioactive due to its natural composition, while cubic zirconia is not.
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Sparkle: Both gemstones shine brightly, but zircon's sparkle is white, similar to a diamond, while cubic zirconia has a rainbow-like sparkle. However, be cautious—other stones like moissanite and strontium titanate also have rainbow sparkles.
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Text Test: Place the stone on a piece of paper with text. Zircon is birefringent, meaning it creates a double image of the text. This effect might be less noticeable if the stone is cut carefully. Cubic zirconia does not show this effect.
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Inclusions: Under a magnifying glass, cubic zirconia looks flawless with no inclusions because it is lab-made. Zircon, being natural, usually has tiny inclusions.
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Weight: Cubic zirconia is heavier than zircon for its size, making its specific density a useful way to distinguish between the two.
By checking these features, you can easily identify whether a stone is zircon or cubic zirconia.
Comparing Zircon and Cubic Zirconia to Diamond
Zircon and cubic zirconia are popular alternatives to diamonds, but how can you tell them apart from diamonds? Here are some simple ways:
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Temperature Test: Diamonds feel warm when worn because they conduct body heat, while zircon and cubic zirconia feel cool to the touch.
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Hardness: Diamonds are the hardest gemstones with a Mohs hardness of 10. Zircon is about 7.5, and cubic zirconia is around 8. While a diamond can scratch zircon or CZ, you wouldn't want to risk scratching your stone.
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Glow Under UV Light: About 30% of diamonds glow under UV light, usually blue and rarely green, yellow, or orange. Zircon and cubic zirconia, however, typically glow mustard yellow or greenish. Heat-treated zircons may revert to their original color with prolonged UV exposure.
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Thermal Conductivity: Diamonds are excellent heat conductors and feel warm when worn, while zircon and cubic zirconia are thermal insulators and feel cold. This test can't distinguish zircon from CZ but helps separate them from diamonds.
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Weight (Density): Both zircon and cubic zirconia are very dense and sink in thick liquids like honey. Diamonds are less dense, making density measurements useful for spotting real diamonds.
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Sparkle: All three stones shine beautifully, but there are differences. Zircon is birefringent, so it doubles images viewed through it. Cubic zirconia has more colorful sparkle (fire) than a diamond.
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Radioactivity: Zircon is slightly radioactive because of natural trace elements, but cubic zirconia and diamonds are not. A Geiger counter can confirm this.
By using these clues, you can tell zircon, cubic zirconia, and diamonds apart without damaging your stones.
Conclusion
So, while Zircon and cubic zirconia might look alike and have similar names, they are very different. The key difference is that zircon is a natural gemstone, while cubic zirconia is lab-made and not considered a natural mineral. Both stones are beautiful, affordable, and convincing alternatives to diamonds.
