01

What to look for

Under 10x loupe or microscope: a dark brown, gray, or discolored spherical zone surrounding a small radioactive mineral inclusion such as zircon, monazite, or thorite.

02

What it means

Radiation halos strongly support natural origin because they require long-term radiation damage around mineral inclusions.

03

Expert move

Look for a perfectly round halo centered on a tiny crystal. In diamond, natural radiation stains can also appear as greenish spots on natural surfaces.