The primary difference between HPHT (High Pressure High Temperature) and CVD (Chemical Vapor Deposition) diamonds lies in their growth patterns and crystal structures, which can be discerned by experts under high magnification. HPHT diamonds typically grow in a cuboctahedron shape with 14 different growth directions, while CVD diamonds grow in a cubic shape with only one growth direction. This difference in growth can occasionally lead to strains in CVD diamonds, though this is rare and requires extremely high magnification to detect.
Detailed Explanation:
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Growth Patterns and Crystal Structures:
- HPHT Diamonds: These diamonds are formed under conditions mimicking the high pressure and high temperature found deep within the Earth. The process results in diamonds with a cuboctahedron crystal structure, characterized by 14 distinct growth directions. This structure is typical of natural diamonds and is replicated in the lab using HPHT methods.
- CVD Diamonds: These diamonds are grown using a chemical vapor deposition process, which involves the deposition of carbon atoms from a gas onto a substrate at relatively low pressures and temperatures. The resulting crystal structure is cubic, with a single growth direction. This method is more controlled and can produce diamonds with fewer impurities, though the unique growth pattern can sometimes lead to internal strains.
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Color and Clarity:
- HPHT Diamonds: Initially, diamonds produced through HPHT methods tend to have a yellowish or brownish hue. However, they can undergo additional HPHT treatments to remove these colors, provided they have a clarity grade of VS1 or higher.
- CVD Diamonds: These diamonds are typically colorless, reflecting the purity of the growth process. However, they can sometimes exhibit brown undertones or spotty inclusions, which might necessitate post-growth HPHT treatment to improve their appearance.
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Production Costs and Efficiency:
- HPHT Diamonds: The process is energy-intensive and requires sophisticated equipment, making it more expensive.
- CVD Diamonds: The CVD process is less costly, quicker, and uses less energy, making it more economical for producers. However, the rapid growth can sometimes result in lower quality gems with undesirable traits like internal graining.
In summary, while both HPHT and CVD diamonds are high-quality and virtually indistinguishable once faceted, their formation processes and initial characteristics differ significantly. Experts can differentiate them by examining their crystal structures under magnification, though this requires specialized knowledge and equipment.
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