under UV light sources. It isn't as hard as quartz, even though it looks a lot like it.
HOW MINERALS FORM You need certain criteria to make a crystal big enough to see. The elements must first be present in sufficient quantities and the right proportions. The physical conditions must also be right for these elements to combine in the right way. They also need to be left undisturbed long enough to grow into their crystalline shape. The existing temperature, level of oxygenation in the environment, pressure, water availability, and pH all determine how a crystalline mineral grows. Time matters because it makes for bigger crystals without something to disrupt the process. Most minerals were floating around as part of the liquidy magma deep inside the earth. As magma rose and cooled, the minerals within it also cooled and solidified. Rapid cooling means you'll get smaller crystals, while slow cooling has the opposite effect. Besides cooling in magma, minerals can form in these other ways: •
The chemical compound can be dissolved in hot water and will crystallize during evaporation or cooling of the water.
•
The mineral can precipitate out of a hot gas, such as you'll see emitted from volcanic vents.
•
Pressure alone can form a mineral during metamorphosis.
•
Exposure to weathering and air can create an oxide mineral.
•
Organisms can contribute substrate for a mineral, such as seashell material or calcium carbonate. Teeth and bones also form apatite crystals that can contribute to mineral formation.
Rocks are essentially collections of minerals. Magma is basically melted rock that can exceed 1000 degrees Celsius. It cools as it makes contact with air, water, or the earth's surface. Minerals can become very large, depending on the circumstances. Granite forms from hot magma that has slowly cooled. The main minerals in granite are: 78
