For the last year, and probably longer, large pieces of colourful crystal, often embedded at one end in a white 'matrix' have been sold on eBay by chinese dealers as 'zircon'.  I purchased two samples and found them to consist of man-made cubic zirconia (zirconium oxide) (easily identified by its high density and distinguished from natural zircon also by the absence of birefringence). I suspect that the 'matrix' is created by fusing some kind of powder to the end of the crystal. I have contacted the dealers and they have continued with their deception. Natural zircon (zirconium silicate) is rare, never found as such large crystals, and is a hundred times more valuable than man-made cubic zirconia.