When the carbonate of magnesia occurring in limestone rises to about 45 per cent, the stone is then called dolomite. It is usually whitish or yellowish in color, and is a crystalline granular aggregate. It is harder than the ordinary limestones, and also less soluble, being scarcely at all acted upon by dilute hydrochloric acid. There is no essential difference between limestone and dolomite with respect to color and texture.