Crystals are formed from minerals that melt or are dissolved in liquids. Crystals in different types of rocks and minerals form one of six different geometric shapes. These shapes were discovered in the 18th century by Abbe Rene Flatly.
A crystal or crystalline solid is a solid material whose constituents, such as atoms, molecules or ions, are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macroscopic single crystals are usually identifiable by their geometrical shape, consisting of flat faces with specific, characteristic orientations.
The scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification. The word crystal is derived from the Ancient Greek word (krustallos), meaning both “ice” and “rock crystal”, from (kruos), “icy cold, frost”.
Most minerals occur naturally as crystals. Every crystal has an orderly, internal pattern of atoms, with a distinctive way of locking new atoms into that pattern to repeat it again and again. The shape of the resulting crystal-such as a cube (like salt) or a six-sided form (like a snowflake)-mirrors the internal arrangement of the atoms. As crystals grow, differences in temperature and chemical composition cause fascinating variations. But students will rarely find in their backyard the perfectly shaped mineral crystals that they see in a museum. This is because in order to readily show their geometric form and flat surfaces, crystals need ideal growing conditions and room to grow. When many different crystals grow near each other, they mesh together to form a conglomerated mass. This is the case with most rocks, such as granite mentioned above, which is made up of many tiny mineral crystals. The museum-quality specimens shown in the images here grew in roomy environments that allowed the geometric shapes to form uninhibited.
The internal arrangement of atoms determines all the minerals’ chemical and physical properties, including color. Light interacts with different atoms to create different colors. Many minerals are colorless in their pure state; however, impurities of the atomic structure cause color. Quartz, for example, is normally colorless, but occurs in a range of colors from pink to brown to the deep purple of amethyst, depending on the number and type of impurities in its structure. In its colorless state, quartz resembles ice. In fact, the root for crystal comes from the Greek word krystallos-ice-because the ancient Greeks believed clear quartz was ice frozen so hard it could not melt.
CRYSTAL SHAPES
CUBIC Diamond is an example of a mineral with a cubic structure.
HEXAGONAL Beryl has a hexagonal crystal shape.
TETRAGONAL Zircon has a tetragonal crystal structure.
MONOCLINIC Gypsum has a monoclinic design.
ORTHOHOMBIC Sulphur has an orthohombic crystal structure.
TRICLINIC Turquoise has crystals in a triclinic shape.
Picture Credit : Google