Can zircon become worn over time?

Yes, zircon is prone to slowly getting worn down, chipped, or abraded over time, especially where the facets meet, and that happens because it is naturally brittle. Even if it has good hardness, it does not have the toughness you really need for heavy daily activity.

On the Mohs scale, zircon generally falls around 6.5 to 7.5, so it is fairly hard yet physically fragile. If it is set in a ring that gets exposed all day and handled constantly, the edge of a cut zircon will keep scuffing, and it will lose its sharp look until it looks dull. Gemmologists call this “paper wear”. To keep zircon’s bright, diamond-like fire and its double refraction, it is better placed in protective mountings, such as pendants or earrings, or kept for occasional wearing rather than everyday use.