my father gave me a stone. the box is marked"carborundum brand" and "razor hone" razor hone is in cursive writing. the box is orange and greyish. the stone is a # 106 and it measures 4"x2 1/2" does anyone have any information on these? what is it worth? how do you use it? ive been using it to sharpen knives with great success...thanks to all of you in advance.