What are "pebble stones?"?

I have a rock and I promised my son I would find out what type of stone it is but the only thing I can find is "pebble stone" when I look it up. It's white with a little yellow on it; the type you find in gardens. Any idea what type of stone this is? Here's a link to a pic I found: a href="http://www.stonedecorative.com/decorative-stones-products/decorative-pebbles.htm#" rel="nofollow"http://www.stonedecorative.com/decorativ…/a - It's under "Distinctive Stones" - it's the white one. Thanks!