I'm thinking possibly travertine which may have formed in between an other fractured deposit of rocks. Travertine is formed by the precipitation of carbonate mineral. But I really couldn't say unless you know the actual location it came from and some geologist or prospector has given names to the minerals formations found in the area and how they came to be formed. Always a lot going on when it comes to rocks. Dang things are everywhere on the ground. Heck next week I gotta get a little more rock at Pioneer sand and gravel to finish a little landscape project my wife kept bugging me to do. The stuff she picked out a believe is called Guernsey Grey that comes from a quarry in Wyoming. Heck that same type of grey rock could have an entirely different name found elsewhere.
I DNT know the actual location..I got it from a house in Mesa az .iwas cleaning out everything was goin to The dump so I kept a bunch of rocks tht I thought were a good find to keep an not take to dump