Jack Black is a tough black slate extremely hard wearing with a hint of quartz in it. It gives a very beautiful sparkling appearance. Its special feature is the straight lines running across the surface. The slate is available in the standard sizes of 30x30cm and 40x40cm and also larger slabs. Random shaped polygonal pieces of flagstone are extremely popular for paving. The sizes generally range from 30x30cm to 60x60cm and the thickness is usually 1.5-3.5cm.