Concrete blocks, also called cinder blocks and cement blocks, come in a wide variety of shapes and sizes. They are made out of a mixture of Portland cement, sand, gravel and water. Generally speaking, there are two kinds of concrete block, hollow and solid.A concrete block is primarily used as a building material in the construction of walls. It is sometimes called a concrete masonry unit (CMU). A concrete block is one of several precast concrete products used in construction.A brick is building material used to make walls, pavements and other elements in masonry construction. Traditionally, the term brick referred to a unit composed of clay, but it is now used to denote any rectangular units laid in mortar.perforated brick (Brit.) A brick or block in which holes passing through it exceed 25% of its volume, and in which the holes are not small (as defined under solid masonry unit, 2); up to three holes, not exceeding 5 sq in.A block can be considered solid if it has a collision box that players, mobs, or other entities cannot move through; those caught inside a solid block may suffocate. The only exception to this is the cobweb, which, although considered solid, can be moved through, albeit slowly.Composition. Concrete blocks are made from cast concrete (e.g. Portland cement and aggregate, usually sand and fine gravel, for high-density blocks). Lower density blocks may use industrial wastes, such as fly ash or bottom ash, as an aggregate. Lightweight blocks can also be produced using autoclaved aerated concrete.For most practical uses in today’s construction there is no difference. Both are blocks made out of cast concrete. Cinder blocks contain fly ash as an aggregate. That being said, most concrete contains fly ash in today’s construction of concrete masonry units.