Pastel Colors range in shades of blue, yellow, red and orange. When my children were young in the 70s & 80s, roadway chalk wasn't available, so they used these rocks, found on my property, to draw on the road.The rocks come in all sorts of shapes and sizes, the biggest rocks weigh between 1 to 2 ounces, most are small and easy to handle.Most of the rock edges are not sharp, all of the rocks are flat which makes them resemble shale.Sometimes, one edge of a rock may not write, however, all you have to do is try another edge on the same rock and usually it will make a mark.You won't receive any rocks that don't make a mark.Some rocks offer more than one color, blue ones especially, while one edge will mark in blue, another edge on the same rock will often mark in yellow or orange.My son digs for the rocks, washes and weighs them. He also tests each rock to make sure it will make a mark before it is packaged. * Recommended use on Concrete or Black Pavement, the rocks can also be crushed for natural pigment uses.*Do Not Use on Chalk Boards, this natural chalk should not be used on chalkboards of any kind, these rocks tend to be much harder than chalkboard chalk and they will scratch normal chalkboards.