Describe the strain pattern of HPHT lab-grown diamonds, if any.

• A. They show clear spiral strain patterns.
• B. They show no strain patterns.
• C. They show uniform concentric rings.
• D. HPHT lab-grown diamonds never show any clear strain patterns.

Answer: (D)

Strain patterns are distortions in the crystal lattice that can show up as colored fringes or lines when a diamond is viewed under polarized light. HPHT lab-grown diamonds are produced in a highly controlled environment with uniform, steady growth conditions and a metal catalyst in a high-pressure/high-temperature chamber. This setup tends to minimize residual stresses in the crystal, so the lattice grows with fewer clear, detectable distortions. Consequently, you typically don’t observe clear strain patterns in HPHT stones, making them appear more uniform under polarized light compared with natural diamonds or other growth methods that can leave visible lattice stresses. There can be other growth features or inclusions, but distinct strain patterns are not a characteristic marker of HPHT diamonds.