Carbonado diamonds, also known as "black diamonds," are unique and fascinating gemstones. Their distinctive characteristics, including their black color and polycrystalline structure, set them apart from other diamonds. But how can you be sure you're actually looking at a genuine carbonado? This guide will walk you through various methods for testing a carbonado diamond's authenticity.
Understanding Carbonado Diamonds: Key Identifying Features
Before diving into testing methods, it's crucial to understand the unique properties of carbonado diamonds:
- Color: Their defining feature is their dark color, ranging from dark gray to black. This is due to numerous microscopic inclusions of graphite and other materials.
- Structure: Unlike typical single-crystal diamonds, carbonados are polycrystalline, meaning they are composed of many tiny diamond crystals cemented together. This gives them a slightly porous texture.
- Hardness: While still incredibly hard, carbonados are slightly less resistant to scratching than other diamond types due to their polycrystalline structure.
- Origin: Carbonados are almost exclusively found in alluvial deposits in Brazil and the Central African Republic.
Testing Methods for Carbonado Diamonds
Several tests can help determine the authenticity of a suspected carbonado diamond. Remember, definitive identification often requires the expertise of a gemologist.
1. Visual Inspection:
- Color and Texture: Examine the stone closely. Does it exhibit the characteristic black color and slightly porous texture of a carbonado? Look for the absence of a single, clear crystal structure.
- Inclusions: Under magnification, you might observe the numerous graphite and other mineral inclusions that are typical of carbonados.
2. Hardness Test:
- Scratch Test (with caution!): While not recommended for valuable stones, gently attempting to scratch the stone with another material can provide a preliminary assessment. A genuine carbonado should resist scratching by most other materials, except perhaps another diamond. Use extreme caution and avoid damaging the stone. This test is unreliable as a sole method of identification.
3. Specific Gravity Test:
- Hydrostatic Weighing: This precise method measures the density of the stone, comparing it to known carbonado density values. This is best done by a gemologist who has the necessary equipment.
4. Diamond Testing Tools:
- Diamond Tester: These devices measure the thermal conductivity of a stone. Diamonds possess exceptional thermal conductivity, a key characteristic that helps distinguish them from imitations like moissanite or cubic zirconia. However, the result may be affected by the many microscopic inclusions in the carbonado's structure.
- Refractometer: A refractometer measures the refractive index, providing information on the stone's optical properties. While not conclusive on its own, it can contribute valuable data in combination with other tests.
5. Professional Gemological Examination:
- Gem Lab Testing: The most reliable way to authenticate a carbonado diamond is through professional gemological examination. A qualified gemologist can use a combination of tests, including advanced spectroscopy and microscopy, to definitively determine the stone's authenticity and provide a certificate of authenticity.
Important Considerations:
- Imitations: There are materials that might appear similar to carbonados. Professional testing is crucial to rule out imitations.
- Cost: Proper testing by a gemologist may incur a cost, but it is essential for valuable stones.
This guide provides a comprehensive overview of how to test a carbonado diamond. Remember that a combination of tests, ideally conducted by a gemologist, provides the most accurate assessment of authenticity. The unique properties of carbonados require careful and thorough examination to confirm their identity.
