It's impossible to tell from the picture - could be fungal, or eggs or nymphs of something. Is the soil in the pot fairly damp and were the stones over that area? If so, I'd remove the stones from the whole pot...

Slow release fertiliser by the looks of it. Were you scraping around in the grit as there appears to be a lot in a small space.

MG, It looks too white to be granular fertiliser - that doesn't usually start out bright white, and turns to greyish brown rather quickly when damp...

Small bits of vermiculite?

Thank you all for your replies. It's a succulent plant in a pot. The soil is dry and gritty, and there's a layer of grit on the top.
The bits were spherical in shape and very white, quite shiny, and they were all together in one one spot, that's why I thought they may be eggs.

I wasn't able to remove them by hand so I have now taken the vacuum cleaner and sucked them up :D I also lost some of the grit in the process !

Probably the wisest thing to do, Hywel, if in doubt, get 'em out... who knows what laid eggs under those stones...

I can't think what it might be Bamboo. It's been in the kitchen for a many weeks but they may have been laid when it was in one of the shelters outside.

Hywel, don't rattle your brain needlessly. I know what you're thinking. Here's an idea that works for me, especially when bringing homemade compost indoors. Try this to get rid of errant seeds, pathogens, bacteria, etc which can wipe out your houseplants like wildfire. I think it's an important step.

Pasteurize Compost. Pour up to 4 inches of your composted soil into a large aluminum baking pan and put a meat thermometer in the center of the tray, deep into the dirt. Place the tray in the oven and keep an eye on the dirt's temperature. Once the center of the dirt reads 160 Fahrenheit degrees, bake for 30 minutes.

Bamboo, looking again you are right - not fertiliser. BG I don't think this is Hywel's home-made compost just something the plant was in.

I think you're right Mg. Nevertheless, something you can do in future.

I'm not sure either Hywel - snail or slug eggs are white, laid in a cluster, often under stones, but they're usually sort of transaparent-ish white and as I recall, a little bigger than these.

I would have said vemiculite or perlight, often used as a moisture retaining addative to commercial composts.

Bulba, that's exactly what it is. Eggs are generally laid in Spring.

Thanks for that idea Bathgate :)

It wasn't perlite etc. I would have seen it when I potted the plant up, and it would also be distributed evenly through all the compost, and not in a cluster in one small area.
It would also be with other things that I had potted up in the same medium but I've never seen it before.

Anyway I've got rid of it now :)

I have seen some kinds of mushrooms start this way, but they're usually not so easy to "suck up".

They didn't really look like a mycelium, they were tiny separate bits.