What happens after the HPHT growth cycle is complete and what shapes can the resulting diamonds have? Expert Analysis

Upon completion of the High-Pressure High-Temperature (HPHT) cycle, the machine’s growth cell is extracted and the newly crystallized rough diamond is carefully removed. The stone undergoes a rigorous cleaning process to strip away the graphite and metallic solvent residues. Depending on the specific temperature and pressure parameters applied during growth, the resulting diamond typically emerges as a truncated octahedron or a hexa-cubic shape.

The post-growth phase transforms a synthesized crystal into a workable gem. Once the rough diamond is extracted from the metal flux and cleaned, it is indistinguishable from natural rough in terms of processing, ready to be cut and polished into a final gemstone.

The Post-Growth Workflow

Extraction and Cleaning

Once the cycle finishes, the diamond is not immediately ready for jewelry. The growth cell is removed from the high-pressure press.

The rough diamond is encased in the solidified mixture of graphite and metal solvent used during growth. This material must be chemically or physically cleaned off to reveal the diamond crystal underneath.

Transition to Cutting

After the rough stone is cleaned, it enters the standard diamond pipeline.

The stone is now ready to be cut and polished. This process is identical to the workflow for natural diamonds, utilizing the same tools and expertise to facet the rough crystal.

Morphology of the Rough Stone

Primary Geometric Shapes

Unlike natural diamonds, which often appear as octahedrons (two pyramids base-to-base), HPHT diamonds have a distinct morphology due to the specific conditions of their growth.

They most commonly form as a truncated octahedron or a hexa-cubic shape. These specific geometric forms are dictated by the precise parameters—temperature and pressure—maintained within the growth capsule.

Surface and Internal Texture

The growth environment also influences the stone's texture.

HPHT diamonds often exhibit a granular structure. Furthermore, because they grow within a molten metal flux, they do not typically show strain patterns, which are common in natural diamonds that endured geological stress.

Understanding the Trade-offs

Metallic Inclusions

While the shape is distinct, the internal clarity of an HPHT diamond carries specific risks related to the growth method.

Because the diamond grows in a solution of molten metal (the catalyst), microscopic droplets of this metal can become trapped inside the crystal. These appear as metallic inclusions, which can look like black, opaque specks or reflect light with a metallic luster.

Magnetic Properties

These metallic remnants can sometimes be significant enough to affect the stone's physical properties.

If the metallic inclusions are large or numerous, the diamond may actually exhibit weak magnetic attraction. This is a unique characteristic often used to identify HPHT-grown stones during screening.

Making the Right Choice for Your Goal

Whether you are evaluating rough stones or finished jewelry, understanding the origin of the diamond helps manage expectations regarding quality and appearance.

• If your primary focus is identifying rough diamonds: Look for the distinctive truncated octahedron or hexa-cubic geometry, which differs from the standard octahedron of many natural stones.
• If your primary focus is assessing clarity in polished stones: Inspect the diamond for metallic flux inclusions, which appear as opaque black specks or metallic reflections distinct from natural carbon spots.

The shape of the rough HPHT diamond is a direct signature of the extreme engineering required to create it, setting the stage for the cutting process that follows.

Summary Table:

Stage/Feature	Details
Post-Growth Process	Cell extraction, removal of graphite/metal flux, and chemical cleaning
Common Rough Shapes	Truncated octahedron, hexa-cubic geometry
Internal Characteristics	Metallic flux inclusions (opaque black specks), granular structure
Physical Properties	Potential for weak magnetic attraction due to metallic remnants
Secondary Processing	Standard cutting and polishing (identical to natural diamonds)

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