Inorganic crystals can be found in a variety of colors and form intriguing shapes as they grow.
Crystals are solids made up of atoms, ions or molecules in a fixed, three-dimensional, geometrical arrangement. Inorganic crystals are not derived from any type of living organism and are composed of some type of mineral. The great variety of naturally occurring, colorful mineral crystals has led them to be called the flowers of the mineral kingdom.
Growth of Crystals
Although crystals can seem to take an endless variety of shapes, they can be categorized into six basic geometric systems based on their molecular structure. As crystals grow, they form a series of structures that result in a fascinating overall shape.
Geometric Crystal Systems
In the cubic, also referred to as the isometric, system, each crystal forms at 90-degree angles, with axes of equal length. This system does not always result in a six-sided crystal. Some cubic systems result in crystals with eight (octahedrons) or ten (dodecahedrons) sides.
Tetragonal crystals are similar to cubic crystals but form with one side longer on one axis. Tetragonal crystals form prisms and double pyramids.
Orthorhombic crystals are similar to tetragonal crystals; however, they form rhombic prisms or double pyramids. The three axes are of different lengths, at right angles to each other.
Hexagonal crystals are six-sided prisms. This system also includes subdivisions called rhombohedral or trigonal. The differences occur in the type of rotation. The system has four axes, three in one plane and equal in length, with the fourth perpendicular to the other three.
Monoclinic crystals look like slanted tetragonal crystals. Like orthorhombic crystals, monoclinic crystals form prisms and double pyramids. Three axes are unequal in length, with two oblique to each other but perpendicular to the third.
The triclinic system forms crystals with asymmetric sides. The result is unusually shaped, often one-of-a-kind crystals. The three axes are of unequal length and oblique to each other.
Crystal Colors
Crystals get their colors from the types of minerals present, which can result in some dazzling hues. For example, quartz is the compound silicon dioxide (SiO2). It forms one of the most common crystals, but it is seen in a variety of shapes and colors. In its pure form, quartz is clear. However, many quartz crystals also include small amounts of other minerals, which impart colors . Rose quartz contains varying amounts of titanium to provide the distinctive pink color that gives this quartz its name. The presence of iron in quartz results in a deep purple color. This can be seen in the gemstone amethyst.
Fluorite is calcium fluoride (CaF2), which is transparent in its pure state. The presence of different hydrocarbons, though, can give fluorite crystals a range of colors, including yellow, green, purple, blue and brown. The choice of colors is virtually limitless among the thousands of different mineral crystals.
Uses of Crystals
Along with being attractive to look at as jewelry or just as decorative items, crystals are used in a number of different ways, including as abrasives, pigments and electronics components.
For example, quartz is one of the most popular crystals for commercial applications. It is used in making glass and as an abrasive for sanding. Quartz watches are synchronized to the vibration of synthetic quartz. Garnet is another crystal commonly used as a sandpaper abrasive. Hematite, a black metallic mineral crystal, is ground and used as a pigment.
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