Dresser Trap Rock is a very hard basalt used by many railroads for track ballast. Although it is great for model railroad applications, it can be used in any miniature model. Choose from a range of sizes to fit the scale you model. From ultra fine to coarse grades, Dresser Trap Rock will work with model railroads, farm dioramas, fairy gardens, doll houses, architect models or movie props. The color is very distinct. It can have hints of blue, red, or purple. In its crushed form, dark gray is the predominate color.