Beats me. We installed a Cararra backsplash about 5 years ago for $3.85 for 3"x6" hand cut subway tile. We went back for more and now the same stuff is $16.+ a square foot. We were blown away. There was no difference at all, as far as we could tell.

we went through this a few months ago selecting the purest white i could find. The prices were all over the map. I looked at thassos but ended up with sivec white which is truly white. It is quite porous so it needs to be sealed often.
Also the color varies from tile to tile but i like that in natural stone.

I am very pleased with how the marble looks in the bathroom. you can search for the thread titled 'bling...'.

Paid about $5 per sq ft for 18x18x1/2 tiles.

With some marbles and granites, there IS no difference. With others, though, there's alot of difference. For example, travertine, bottocino, and crema marfil are three stones notorious for the way they fracture on veins, sometimes just from their own weight when picking them up. This problem will be much more prevalent in some lots rather than others. Guess which one's you'll find at the big box stores? As for granites, the same goes for coloring. My favorite stone of all time is the perfect example. Blue pearl-- it can run from a bright sapphire blue, to almost a cadet grey, depending on the lot your stone comes from. It's very rare that you'll see prime grade blue pearl at HD.

As for pharaoh's example with the thassos, just like with blue pearl, there are actually different grades of the stone, from stone that has some veining to it, to stone that has occasional markings (almost resembling stains) to clear, which is a pure brilliant crystaline white. You'll never see clear thassos at the box stores.

pharaoh-- you should've kept looking:

Pharoah, where did you get your white tiles? I like them, though I think we do want some veining. i just don't want really gray Cararra--I want white with some gray streaks. The whitest tiles I saw are at HD--Venetian White and Crystal--both special order and Grecian (I think this is in stock). The most expensive was $5.99.

Bill, would I be crazy to buy from HD? I also like the Cararra from Tile Shop, though I have heard some stories of it being yellow.

kelleg,
I bought mine at http://www.stonemart.com/ in north hollywood. I would recommend you buy a sample of each and test it for staining, scratching and color. (cool white vs warm white)

bill,
i did look far and wide for clear thassos including design stores. here in LA we have hundreds of stone suppliers. even thassos that was $12.50 per sq ft had inclusions in it! the seller recommended i buy double of what i needed and use only the purest ones... remember i am DIYer on a budget :) (well except for the swarovski accents)

Pharaoh-- you won't find clear thassos for less than about 18.00 a foot, and that's on a GOOD day. That's about what I'd pay for it.

kelleg-- I'd be highly suspect of carrara from HD. The reason is that low grade carrara will contain iron in it, which is what gives it the yellowish color. It's also what reacts, especially with high chlorine content city water, and end up making the stone look like it's rusting (because it IS). Get your stone from a reputable stone dealer. You're going to pay more for it, but you'll be happier with it in the long run.