The voids are remnants of small gas bubbles during crystallization. The internal texture probably represents mineralization within the voids. See if it has a concentric texture, then it is definitely mineralization after the formation of the void.

I have seen voids in zircon and I interpreted them as places of former mineral inclusions that were later dissloved.

Hi There,

Be aware that you probably have the BSE turned up nice and high to get your images, so make sure they are actually voids (e.g. use SE imaging) and not mineral or melt inclusions.

If they are voids of that scale then one guess would be volume expansion from alpha decay. This can cause a variety of cracked textures, which if reannealed can appear as voids within the grain.

The next obvious one, as mentioned above, would be fluid alteration. dissolution-reprecipitation for example will tend to expel trace elements and leave behind a more 'pure' grain, which will therefore have a lower modal volume. I would reccommend looking at some papers from Thorsten Geislers zircon work, or the Frank Tomascek paper in JPet on Syros zircons for good textures of this kind.

As always, an image would be good, and extra info such as SE, CL, rock type etc

Rich

Zircons of this type are not rare, they crystallize simultaneously with the liberation of the gas phase from the rapidly decompressed melt.

Dear All, Thank you very much for the valuable answers.... And I gave more attention on those grains. I made EPMA spot analysis on those void like structures... surprisingly it was not voids... as Dr. Richard Taylor emphasized in his answer... they were zircon crystals.. and the Total of Si, Zr, and Hf quantity is almost 100%. mostly, seems like pure zircon crystals....

Were they really perfectly rounded?

That is impossible to determine. But seems rounded. Some of those tiny crystals are not rounded...