Onyx Vs Black Diamond

6 min read Jun 30, 2024
Onyx Vs Black Diamond

Onyx vs. Black Diamond: Understanding the Difference Between These Two Gemstones

The world of gemstones is full of dazzling beauties, each with its unique characteristics and allure. Two stones that often get confused due to their striking black appearance are onyx and black diamond. While both are prized for their dark elegance, they are fundamentally different in their origins, properties, and value.

Onyx is a type of chalcedony, a microcrystalline variety of quartz. It is known for its banded structure, with layers of different colors forming intricate patterns. While black onyx is the most popular, it can also be found in brown, white, and even red hues. Black onyx, specifically, is formed through the deposition of silica in layers within volcanic rocks.

Black diamonds, on the other hand, are simply diamonds that possess a very deep, dark color. Diamonds, as we know, are formed deep within the Earth's mantle under immense pressure and heat. Their color comes from impurities trapped within their crystal structure. Black diamonds, also known as carbonado diamonds, are exceptionally rare and are found primarily in Brazil and the Central African Republic.

Physical Differences Between Onyx and Black Diamond

Let's delve deeper into the key distinctions between these two gems.


  • Onyx is relatively softer, scoring 6.5 to 7 on the Mohs Hardness Scale.
  • Black diamonds, being diamonds, are the hardest natural mineral on Earth, scoring 10 on the Mohs Hardness Scale.


  • Onyx usually exhibits a waxy luster or a glassy luster.
  • Black diamonds, due to their internal structure, have a brilliant luster.


  • Onyx is opaque, meaning light cannot pass through it.
  • Black diamonds can range from opaque to semi-transparent, depending on the concentration of impurities.


  • Onyx is relatively inexpensive, making it a popular choice for jewelry and decorative items.
  • Black diamonds, due to their rarity and hardness, command significantly higher prices, often exceeding the cost of regular diamonds.

Onyx vs. Black Diamond: Uses and Applications

Both onyx and black diamonds have distinct applications, influenced by their unique properties.


  • Jewelry: Onyx is commonly used in rings, earrings, necklaces, and bracelets. Its affordability and durability make it ideal for everyday wear.
  • Decorative Items: Onyx is frequently used in sculptures, figurines, and decorative boxes due to its rich color and intriguing patterns.
  • Cameos: The banded structure of onyx lends itself beautifully to carving, making it a popular material for cameo art.

Black Diamonds:

  • Jewelry: Black diamonds are prized for their unique allure and are often set in bold, modern designs.
  • Investment: Due to their rarity and durability, black diamonds are considered a valuable investment.
  • Industrial Applications: The extreme hardness of black diamonds makes them useful for drilling, cutting, and polishing tools.

Onyx vs. Black Diamond: Identifying the Difference

The most reliable way to distinguish between onyx and black diamond is through testing their hardness and luster.

  • Onyx will easily scratch with a steel knife, while black diamonds will resist any scratching.
  • Black diamonds will exhibit a significantly brighter luster compared to onyx.

However, if you are unsure, it is always best to consult a qualified gemologist for professional identification.


Onyx and black diamonds, despite their similar black color, are distinct gemstones with unique origins, properties, and values. Onyx is a more affordable and versatile material, suitable for jewelry and decorative items, while black diamonds are rare, valuable, and often used in high-end jewelry and industrial applications. Understanding the differences between these two gemstones will help you appreciate their individual beauty and choose the one that best suits your needs and preferences.



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