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Crystals are found in everything from snowflakes to table salt. They can also be created in your kitchen with a simple science experiment.
This micrograph shows the simplest form of snowflake. This tiny crystal was captured near the North Pole where the temperature was about -35° C and the atmosphere was extremely dry. Consequently, as the snowflake came down through the lower atmosphere, there were few water molecules in the air to attach to the surface lattice of the crystal. It therefore remained simple and uncomplicated. Courtesy of Dr. Nirmal Sinha, NRC.
Crystals are naturally occurring structures. The word ?crystal? comes from the Greek word meaning ?clear ice.? Crystals are often transparent, but not all transparent substances are crystalline. For example, glass is transparent, but it has an amorphous (shapeless) structure, not a crystalline one.
Each crystal is a characteristic unit composed of atoms or molecules arranged in a lattice structure. A crystalline structure is built from these repeating units, which can be compared to building blocks. Perfectly shaped crystals are polyhedrons with many sides, such as tetrahedrons that have four triangular faces.
Did you know?
Snowflakes are collections of ice crystals. The individual ice crystals of snowflakes have a hexagonal, or six-sided, structure due to the natural arrangement of hydrogen and oxygen atoms in water (H2O).
As water vapour in the atmosphere cools slightly below freezing and collects on ?seeds? of dust, sand or other microscopic substances, ice crystals form in clouds about 10 kilometres above the surface of the Earth. Snow crystals develop as water vapour freezes on the first seed crystals. As these crystals grow, passing through layers of clouds saturated with water, they become heavier and fall to Earth.
The many shapes of snow crystals
Skiers are very familiar with the different types of snow and they wax their skis accordingly. Depending on the temperature and humidity at the time of formation, snow crystals occur in various forms:
- hexagonal plates
- stellars
- columns
- needles
- dendrites
- prisms
- irregular crystals or powder snow
Snow crystals occur in forms ranging from prisms to needles to dendrites with delicate branches. Illustration: SnowCrystals.com
Science activity
Science is all around you! Discover something new about crystals.
