The sand has been spread out on to a piece of plain paper to show the fine grains. The lumps will disappear when shaken.
You do not need much when modelling as I also mix it with coarser grained sand. This small plastic container will last for ages.
It is possible to buy a similar product used by children to make coloured sand pictures, you apply the sand over a thin layer of craft glue. However this source is much cheaper.