Quartzite is the perfect choice. Click on this thread and you will see a picture of ILoveRed's kitchen with white cabinets, and a brown island. I don't remember her quartzite's name. You can ask her- it's a new and active thread.

https://www.houzz.com/discussions/which-grout-for-backsplash-dsvw-vd~5698896#n=11

Regular homeowner gal here. Congrats on such a huge undertaking! I get that different cab colors are pulled together with matching countertop. Wonder if it makes sense to consider the dark island base as a separate piece of furniture, therefore not subject to the "rule." Floors should also have a unifying effect. Have you considered granite? Not mentioned. There is so much in color variations in granite out there. Much less porous that marble, I understand. Mine from 10 years ago is darker shades that I now wish I had gone with lighter tones with white cabinets. Should be plenty with white/pale background (white kitchens are everywhere!) with gray specs AND dark specs to pull together. Wish I could think of the name of one with white background with gray specs and a reddish purple/grape shades of specs...one of the more common versions, so a little less expensive than some, but I like the warmth the specs give it. Would really pull the red/purple hints of your island color but easily complement white cabs. Not as "busy" as it sounds. Color of specs vary in natural stone. Might take looking at specific cuts at a yard to find the color inclusions you like. And, yes, gray would work very well with white and cherry, and soapstone is a lovely natural choice. Don't know about its porosity. I confess, I am also not familiar with quartzite. Good luck!

no problem! Use leathered or honed black granite counters with white quartzite, I love it, do it all the time in my own home and many of my clients. Works well, no maintenence! Quartzite comes in whitish, greenish- toned whitish, Creamy warm toned white and greyish white. will look great with warm stain and painted cabinets.

Since your island is already different I’d keep countertops the same. Looks like a good sized kitchen that will have enough going on without main elements all being different.

Here is the thread where I Love Red finds here quartzite. It's the the first slab she shows, scroll down a bit- she goes shopping again and finds a different one. I didn't see the name though.

https://www.houzz.com/discussions/does-this-quartzite-look-good-with-my-white-dove-cabinetry-dsvw-vd~5413801

You might want to look into fantasy brown - its beautiful and goes with greys and beiges...

Is the only sink the one in the bay window and is your fridge across the room from the sink? If so, are you ok with your island being a barrier between your sink and fridge?

As for the quartzite, I would go with Taj Mahal since it will pick up the warm tones of the island as well as the grays you're hoping to bring in.

Taj can vary a lot in the amount of beige or gray in it. Go look at actual slabs and if you see one that works, put a hold on it. Also, be aware that the color of your lightbulbs will greatly effect how beige or gray the stone looks in your kitchen. I'm not lightbulb expert, but others will chime in with advice, I'm sure.

With all of those angles, the best choice for this kitchen will not be a stone with a lot of linear movement unless you are prepared to seek out your area’s best fabricator, and also are prepared for extra expense. If you do choose a stone with a lot of movement, be sure to choose bookmatched pieces, and that will mean extra slabs. Budget may not be a big factor for you, but extra slabs and the best fabricator can get even more pricey, when you are already looking at a high priced stone. So if you need to keep to a lower cost option, something like Cambria Marwell or Huntley could work better, with less waste.

Marwell

Huntley

Agree with @Cook's Kitchen. If you're going to do a bolder patterned quartz, use it for the island only, then do a solid color for the perimeter cabinets. The other option might be to make the island feel more like a furniture piece and do a walnut butcher block/furniture finish for the counter. If you go this route, I might keep the island white, or pick another darker paint-grade color.

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Cpartist, no there is a prep sink in the island on the end near the fridge.

Oh good! Only thing is I wouldn't have it on the end. Why?

You take your food and veggies out of the fridge and where do you put them before you wash and prep them? I would move the sink over so you have at a minimum 1' of space to the left. 15" would be a lot better.

I’m afraid the Taj Mahal brings in too much brown, no?

It depends on the slab you find. You really need to go to stone yards to find the slabs. I believe it was NewEnglandGal who found a slab with more grays than browns just recently?