Rock Basics Rock is the hard solid material all around us Huge masses of rock make up the solid part of Earth But rocks come in smaller sizes too from boulders and pebbles to sand and clay BOULDERS SAND PEBBLES 6
Whatever their size rocks share something in common they all consist of minerals Most rocks contain two or more minerals Sometimes though a single mineral makes up a rock Minerals in many rocks are easy to see But minerals can be very tiny as well People often mine rocks for the minerals they contain 7
Minerals Unique in Structure and Make-up Minerals are chemical substances commonly found on Earth There are thousands of known minerals However only about 25 make up most types of rock Each mineral whatever its location has a specific chemical make-up Its ingredients include elements the most basic chemicals found in all matter Minerals consist of one or more elements 8 Minerals fit into seven main groups based on their chemical make-up Amateur geologists collect mineral samples like this Galena for their beautiful colors and interesting crystal shapes
Every mineral also has a unique structure It stays the same whatever the mineral’s size This three-dimensional shape comes from the mineral’s elements Each one has its own building blocks called atoms When elements combine in a mineral their atoms arrange themselves in a specific way The atoms in some minerals arrange themselves in an orderly pattern These minerals take form as crystals A crystal is a solid with many repeating flat surfaces Minerals that do not form crystals grow in a less orderly way Their atoms have a less orderly arrangement too 9
