Section 11.2 Rocks & Minerals
Rocks and Minerals
Rocks and minerals are naturally occurring substances found in the earth’s crust. Rocks are made up of one or more minerals, while minerals are pure substances with a definite chemical composition and crystalline structure. A mineral may be a single element such as copper (Cu) or gold (Au), or it may be a compound made up of a number of elements. About 2,500 different minerals have been described. Rocks are made up of one or more minerals but it does not have a definite chemical compositions. Minerals are classified based on their chemical composition and crystal structure. Some common minerals include quartz, feldspar, mica, calcite, and pyrite Figure 11.2.2. Minerals have a wide range of uses, from building materials to electronics and jewelry.
- Quartz: is composed of silicon and oxygen atoms in a continuous framework of \(SiO_4\) silicon-oxygen tetrahedra, with each oxygen atom shared between two tetrahedra, giving an overall chemical formula of \(SiO_2\text{.}\) It is a six-sided prisms with pointed ends (known as hexagonal crystals) with no cleavage. The color of quartz can vary depending on impurities, with clear quartz being colorless, while other colors such as pink, purple, and brown can be caused by trace amounts of other elements.
- Feldspar: is a group of minerals that are the most abundant minerals in the Earth’s crust comes with range of color, harder than glass and softer than quartz. The feldspar group is divided into two major groups: alkali feldspar and plagioclase feldspar. Alkali feldspar includes minerals such as orthoclase and microcline, while plagioclase feldspar includes minerals such as albite, anorthite, and labradorite.
- Mica: Mica is a group of minerals that is found in rocks such as granite, gneiss, and schist. It is composed of silicate minerals with varying amounts of aluminum, potassium, magnesium, iron, and water. Mica is known for its unique properties, such as its ability to split into thin, flexible sheets, its excellent insulating properties, and its resistance to heat and chemicals. These properties make it a valuable material in a wide range of industries, including electronics, construction, cosmetics, and paint manufacturing.
- Calcite: Calcite is a carbonate mineral that is commonly found in sedimentary rocks such as limestone and marble. It is composed of calcium carbonate \((CaCO_3)\) and it is relatively soft. Calcite has many unique properties, including its ability to exhibit birefringence, a phenomenon where light passing through the mineral is split into two different rays, which can produce a double image. It is also fluorescent under ultraviolet light, and some varieties can even exhibit phosphorescence, meaning they continue to glow after the light source is removed.
- Pyrite: Pyrite, also known as "fool’s gold," is a common mineral that is found in sedimentary, metamorphic, and igneous rocks around the world. It is composed of iron sulfide \((FeS_2)\) and has a metallic luster, giving it a shiny, brassy-yellow appearance. Pyrite is relatively hard and can scratch glass. It is often found in association with other minerals, such as quartz, calcite, and fluorite. Pyrite has been used as a source of sulfur for the production of sulfuric acid, and it is also used as a decorative stone and in jewelry. One of the most notable properties of pyrite is its ability to generate sparks when struck against steel or another hard surface. This property has made pyrite a popular material for use in flintlock firearms and other types of fire-starting tools.
