Inside a mineral, atoms arrange themselves into a specific, repeating pattern called a crystal lattice or crystal structure. The smallest three-dimensional arrangement within the lattice is called a "unit cell," which is duplicated over and over again symmetrically. At the level of the everyday world, minerals that are growing without outside interference tend to form crystals that resemble their underlying crystal structures. Scientists call that kind of general, typical appearance a "crystal habit." Of course, conditions that existed during a mineral's formation or crystal growth may change its habit, but geologists still find this attribute to be a useful tool for identifying minerals. Scientists use more than three dozen adjectives to describe crystal habits. For example, natrolite and rutile can be acicular, or needlelike; quartz often forms hexagonal prisms; pyrite and halite typically crystallize as cubes; and mica is foliated or lamellar (layered).

Certain rare elements such as beryllium, tantalum, lithium, and yttrium occur in small quantities scattered around the world, rather than in rich mineral veins that are easy to mine. The economic importance of these elements, however, has grown substantially over the past few decades, as scientists and engineers have found new ways to use them. For example, tantalum, found primarily in the mineral tantalite, helps miniaturize the electronic components inside computers, gaming consoles, and cell phones. Lithium powers those portable devices by making batteries last longer. Beryllium, found in more than 100 minerals, goes into lightweight structural components of fighter jets, guided missiles, and spacecraft. When added to diesel fuel, cerium lowers the noxious emissions from trucks. Gallium and indium, two elements that are considered electrical semiconductors, go into light-emitting diodes (LEDs). Yttrium is a key ingredient in medical lasers.

For example, the mineral bastnasite (or bastnaesite), which contains cerium, lanthanum, and yttrium, was discovered in Sweden and occurs. The economic importance of these elements, however, has grown substantially over the past few decades, as scientists have put them into many high-tech devices. Cerium added to diesel fuel helps trucks run with fewer noxious emissions; scandium, alloyed with aluminum and other metals, makes lightweight lacrosse sticks and components for fighter jets; yttrium is a key ingredient in medical lasers.