Ratnapura alluvial zircon (Jargon): distinguishing high zircon from low metamict stones?

Sri Lankan zircon (ZrSiO4 / Jargon) occurs in three distinct structural states depending on historical self-irradiation from trace uranium and thorium impurities. "High" zircon has an intact tetragonal crystal lattice, showing extreme birefringence (0.059), refractive index over 1.92, high density (~4.70), and sharp doubling of rear facet edges under a loupe. Over millions of years, alpha-particle radiation breaks the crystal lattice down into an amorphous glass-like "low" or metamict state. Low zircon displays lower density (~3.95-4.10), minimal birefringence, and a dull, cloudy olive-green body color.