- Define mineral.
- Describe the basic structure of the atom.
- Derive basic atomic information from the Periodic Table of Elements.
- Describe chemical bonding related to minerals.
- Describe the main ways minerals form.
- Describe the silicon-oxygen tetrahedron and how it forms common silicate minerals.
- List common non-silicate minerals in oxide, sulfide, sulfate, and carbonate groups.
- Identify minerals using physical properties and identification tables.
The International Mineralogical Association in 1985 defined “A mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes.” This means that the calcite in the shell of a clam is not considered a mineral. But once that clamshell undergoes burial, diagenesis, or other geological processes, then the calcite is considered a mineral. Typically, substances like coal, pearl, opal, or obsidian that do not fit the definition of a mineral are called mineraloids. A rock is a substance that contains one or more minerals or mineraloids. As is discussed in later chapters, there are three types of rocks composed of minerals: igneous (rocks crystallizing from molten material), sedimentary (rocks made of products of mechanical weathering (sand, gravel, etc.), chemical weathering (things precipitated from solution), and metamorphic (rocks produced by alteration of other rocks by heat and pressure.
- 4.2: Chemistry of Minerals
- Rocks are composed of minerals that have a specific chemical composition. To understand mineral chemistry, it is essential to examine the fundamental unit of all matter, the atom. Matter is made of atoms. Atoms consist of subatomic particles—protons, neutrons, and electrons. A simple model of the atom has a central nucleus composed of protons, which have positive charges, and neutrons which have no charge. A cloud of negatively charged electrons surrounds the nucleus.
- 4.3: Formation of Minerals
- Solutions consist of ions or molecules, known as solutes, dissolved in a medium or solvent. In nature, this solvent is usually water. Many minerals can be dissolved in water, such as halite or table salt. The Na+1 and Cl-1 ions separate and disperse into the solution. Precipitation is the reverse process, in which ions in solution come together to form solid minerals. Precipitation is dependent on the concentration of ions in solution and other factors such as temperature and pressure.
- 4.4: Silicate Minerals
- Minerals are categorized based on their composition and structure. Silicate minerals are built around a molecular ion called the silicon-oxygen tetrahedron. A tetrahedron has a pyramid-like shape with four sides and four corners. Silicate minerals form the largest group of minerals on Earth, comprising the vast majority of the Earth’s mantle and crust. Of the nearly four thousand known minerals on Earth, most are rare.
- 4.5: Non-Silicate Minerals
- The crystal structure of non-silicate minerals (see table) does not contain silica-oxygen tetrahedra. Many non-silicate minerals are economically important and provide metallic resources such as copper, lead, and iron. They also include valuable non-metallic products such as salt, construction materials, and fertilizer.
- 4.6: Identifying Minerals
- Geologists identify minerals by their physical properties. In the field, where geologists may have limited access to advanced technology and powerful machines, they can still identify minerals by testing several physical properties: luster and color, streak, hardness, crystal habit, cleavage and fracture, and some special properties. Only a few common minerals make up the majority of Earth’s rocks and are usually seen as small grains in rocks.
Thumbnail: A ball of lustrous, royal-blue cavansite blades is set on a starkly contrasting snow-white crust on basalt matrix on this fine specimen from recent finds at the Wagholi Quarry of India. Image used with permission (CC-SA-BY 3.0; Rob Lavinsky from iRocks.com).