On the outside of the plasma membrane? acts as signals or makers to cells recognize one another

Outside the plasma membrane there is presence of glycoprotein which is a series of polysaccharides to form the cell coat and is used for ID or cell recognition. Each individual has a unique special code for the glycoprotein.

the rocks are classified by the geological process they are formed by. the three main groups of rocks are igneous, metamorphic, and sedimentary. minerals are not they are classified under the chemical classes they are in. these groups include silicates, sulfates and carbonates.