I would call the 10½" white block a ½ snowball.
http://www.straw.com/quilting/articles/snowball1.html
this link shows you how to do the snowball using all 4 corners. Do a trial block to make sure you have the correct size for your corner square (which makes your triangle). Scroll down to the bottom of the page for the tut, the first ½ of the page is blank. Happy Quilting