tucson: I need to know so I can do a project for chemistry class.|||The regular soil around there might be clayey. you can ask the Tucson Botanical Garden or any local nursery or local garden forums. Clay soil is so common, that it is not something that you find for sale. It is everywhere. you can find it where you find puddles<<on the dried puddle, it is the smoothest dirt. it is not sand but more like powder. if it is wet, then it is mud and still smooth but sticky too. sources of Tucson garden help: http://www.tucsonnewcomer.com/features/g鈥?/a> Clay has little pieces that fit close together. those surfaces make nice smooth pottery. and solid bricks. People dig up clay soil and then use it to make bricks and pottery and also people sell clay for those purposes. here is a craft supply shop: Michaels-Arts & Crafts (520) 293-0430 4070 N Oracle Rd Tucson, AZ 85705-2720 and you can research "pottery supplies" if you want because there will be a lot in your area. telephone books and the internet are good. here is a site with recipes to make your own "clay": http://familycrafts.about.com/od/clayrec鈥?/a> In terms of texture, clay soil is made of particles smaller than sand, less than 0.002mm in size. "Clayey" soil must have at least 30% clay particles. Clay particles are the dust of a thousand ingredients and so they have many nutrients. Since it is composed of the smallest and lightest particles, it will take the longest to settle out of solution<<<the heavier particles will settle to the bottom of a glass of water much more quickly than clay particles will settle. Clay soil is usually acidic but alkaline soils can be very clay like as well. Desert clays are often alkaline>>>maybe Tucson's desert is like that. Alkaline clays are used for cement>>like lime. lime is powerful in many ways. and it is also sold as fertilizer and soil amendment for areas that are acidic. clay soil can have a neutral pH too but usually a whole region will have the same type of soil..we do not find acidic soil here on this one street corner lot and then alkaline soil on the next street. and it can be black or brown or red or orange or yellow or white pH can be related to colors, for instance alkaline soil like lime is usually white or sometimes yellow. Acidic colors are red and orange<<they have lots of oxidized iron. and clay is needed to make up the best of garden soils/loams. You can buy special pure clays from all over the world. You can buy them by the ounce and such because women use it for face treatments. i have seen it from $4.50 to $13 per oz (USD). for clay soil in your area you only need to look around and dig around and examine the texture of the soil. There will probably be a few layers and a few colors. When you see how many layers and what colors then take notes. Then you will be able to find out all that you need. The soils will be documented on the web and at university sites. they will be documented according to color and depth of layer and number of layers and thickness of layers. and if you bring samples to various local authorities, those people will give you opinions that you can weigh for truth and then include in your studies. sometimes the local agricultural extension office would do free tests but it is rare these days, you can check with your area's extension so there you go, dig around for smooth powdery dirt <<not sand, but powder or sticky gooey puddles if it's raining down there <<not regular sand that would fall apart in a sand snowball but sticky smooth make some pottery type clay the pH is easy to find out, btw, you can use paper test strips from science class or get some at the local nursery/plant supply place (they can cost almost $10 USD sometimes). or you can make your own strips with a red cabbage. search "homemade pH test red cabbage"