Catalog Number:
40925 -DSP
Specimen Count:
1
Special Instructions:
Only available digitally
Location:
Collection Wall

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).

Since antiquity, humans have made pottery from clay, which consists of fine particles of silicate minerals. Kaolinite is an aluminum silicate mineral, and it is the main component of porcelain, a particularly hard type of ceramic. Clay, which is used to make other types of pottery, may contain silica and grains from sedimentary rocks. Quartz, also referred to as silica or silicon dioxide, is a key component of another important solid material: glass. In the ancient Middle East, humans made glass by heating silica with alkali that was made from the ashes of plants. Other minerals such as calcium, lead, calcium, and manganese were added to improve the glass. Metals and metallic oxides were also added to color the glass or to make it clear, since natural glass tends to be slightly colored from impurities in the sand. Ruby red is made from powdered gold, while an orangey-red is produced by copper oxides. If the glass with copper oxide is heated too much, it will turn green. Cobalt and iron can make blue glass, and manganese is used for purple. Antimony or manganese oxide will produce clear glass. Glass for specialized purposes, like cookware and optical instruments, may require additives, such as boron oxide or lead oxide.