Target: I will be able to describe what is needed for crystal growth and describe crystal structure. © Charles Falco, Science Source from Photo Researchers

1. Crystallography - The science of crystal structures and how they are made.

2. For crystallization to occur, 2 things must happen! Nucleation- dissolved molecules gather and form clusters – nuclei (you can’t see them) Crystal growth – nuclei grow and form crystals

3. Crystal: a three-dimensional repeating pattern

There are 2 things to notice: The pattern of repetition (the lattice type) What is being repeated (the unit cell) 4. Unit Cell: the smallest unit that demonstrates the full symmetry of a crystal.

5. Lattice - The 3 dimensional pattern formed by repeating unit cells

Saturated Solution Water molecules Borax molecules

6. Symmetry and form of a crystal are determined by the shape of that unit cell.

Ice crystal photo from CalTech World Book diagram by Linda Kinnaman

Borax

The Science Behind the Fun Snow Flake Borax Crystal Borax is an example of crystal - "a solid with flat sides and a symmetrical shape because its molecules are arranged in a unique, repeating pattern." Every crystal has a repeating pattern based on it's unique shape. They may be big or little, but they all have the same "shape". Salt, sugar, and Epsom salts are all examples of crystals. Salt crystals are always cube-shaped while snow crystals form a six-sided structure.

How do the Borax crystals grow How do the Borax crystals grow? Hot water holds more borax crystals than cold water. That's because heated water molecules move farther apart, making room for more of the borax crystals to dissolve. When no more of the solution can be dissolved, you have reached saturation. As this solution cools, the water molecules move closer together again. Now there's less room for the solution to hold onto as much of the dissolved borax. Crystals begin to form and build on one another as the water lets go of the excess and evaporates.

NaCl (B1) http://cst-www.nrl.navy.mil/lattice/struk/sc.html Photo courtesy of Cameron Jones NaCl (B1) http://cst-www.nrl.navy.mil/lattice/struk/sc.html

Ga4Ni3 Tungsten Carbide http://cst-www.nrl.navy.mil/lattice

Gypsum’s chemical formula is CaSO4•2H2O World Book photo courtesy of the Field Museum of Natural History, Chicago

Quartz Field Museum of Natural History, Chicago

Crystals come in all sorts of colors! Amethyst (purple) Topaz (blue, various) Emerald (green) Topaz (blue) Tourmaline (watermelon, black) Ruby (red) Gold (yes, it can crystalize!)

What’s wrong with these gypsum crystals? What is its magnification? © National Geographic