I thought all sand was silica? It will be fine, but I'. assuming you mean just used to lighten the soil!

If you are thinking of the silica sand used in ashtrays, that is probably too fine to help much in soil conditioning. I would use a grittier type, such as play sand or well washed builder's sand. Ideal would be horticultural grit, but that can be hard to find, especially in useful quantities.

How fine is the grit you mean Tug? The grit i have is quite coarse, and wouldn't convert soil to a sandy one. If there's a finer one it wold be useful.
A good coarse sand is Calais if you can find it.

Where was it that you want to grow carrots? They will be happy in any friable soil if you are growing in the ground. If you are growing stump-rooted carrots or baby carrots in a large trough then sifted garden soil with a little bone meal will do the trick. Do not mix with play sand or builders' (soft sand) as this will block the drainage. Horticultural sharp sand is best for opening up the compost as it contains no salt.

Well, the one I am thinking of has grains hovering around .5 to 1 mm in diameter. The brand I sell is labelled "horticultural sand", but when I described it on this site years ago, I was told that it was called grit in the UK.
Jimmy, sharp sand would be the thing, if you can find it, but the time I described what I was looking for, I had already contacted a half dozen sand and gravel suppliers in Phoenix for "sharp sand" as recommended by all the gardening shows running then, and was told that they had never heard of such a thing!
Builder's sand needs to be salt and lime free, because of the effect of those impurities on mortar, and generally runs around .2 to .5 mm particle size. Play sand varies some, but is usually a mixture of particle sizes, and works adequately at conditioning clay soil.

In the UK, builders' sand or soft washed sand is used in mortar for brick or block work. Sharp is coarser and is used in concrete and rendering and can be dredged from the sea and washed. Horticultural sand is sharp sand that has neither lime or salt as it is dug from the ground often from ancient river beds. Then there is grit sand and horticultural grit of different grades.