Why is clay rare? [closed]

If you made those chunks (new world or explored new area) during 1.6, clay was bugged and only occurred when the X coordinate equaled the Z coordinate. New chunks in 1.7 should be unaffected by this bug, so you can explore further in an existing map, causing more chunks to be generated, or start a new world.

In the future, I think the amount of clay was going to be upped, as Notch felt it rarer than desired.

It's technically quite common, it just has very specific requirements. It must be in sand, and because there is not much sand (compared to dirt and stone, the other two main blocks) there are not many chances to be generated. Also most of the sand is found underwater, so any clay generated there may not be seen. And a bug from 1.6 only allowed it to be made where coordinate X=Z but this is now fixed.

It does not require water to be spawned but because shores have more unexposed sand, there is the best place to find it.

Now in 1.8.1 clay is much more common! Just look at a river or lake that has sand in it. Look for clay in the deep parts. You should be able to find at least 20-30 pieces of clay in an area like that. I hope this helped.