Crystals

Crystals A crystal is a solid in which the atoms are

arranged in orderly, repeating patterns. Crystalline structure can be seen either

on the inside or the outside of a mineral. Minerals that form with large amounts of

space are able to arrange themselves in crystal form on the outside.

If a mineral forms with limited space, the crystal structure is seen on the inside. We cannot see this with the naked eye.

Crystals from Magma

Magma is hot melted rock. (when it reaches the earth’s surface it’s called lava)

When magma cools it forms crystals

The rate at which the magma cools determines the size of the crystals

These are all pictures of granite.Why do they all look different?

Crystal SizeThe elements present in the

magma will determine which minerals form

The slower the magma cools, the larger the individual crystals

The quicker the magma cools, the smaller the individual crystals

Crystals from SolutionAnother way we can get crystals

is from a solutionRemember, a solution is a mixture

of two or more things that are not chemically combined

Sea water is a solutionWhen the water evaporated,

crystals are left behind.

Cubic Crystals

Cubic CrystalsCubic crystals have all 90 degree

angles with all sides of equal length

Examples of cubic crystals

Galena

Cubic Crystals

Halite

Halite

Hexagonal Crystal

6-sided crystal

Sturmanite

Hexagonal Crystals Quartz

Tetragonal CrystalsMuch like the cubic,

except one side is longer than the others, like a rectangle.

Zircon is a good example

Orthorhombic Think of this

as a brick. It’s like the last one, a rectangle that has been flattened so that its thicknesses are different.

Orthorhombic has all 90° angles still. The rectangle is flattened either a little or a lot, as seen here in a sample of barite. All 3 (pairs of) sides have different lengths.

MonoclinicTake the ‘brick,’ orthorhombic,

and slide it askew so that only one angle is left at a 90° angle

Orthoclase is an example of a monoclinic crystal shape

Monoclinic crystal: Orthoclase

Triclinic This is an unsymmetrical as a mineral can

get No 90°angles Rhodonite is an example

More rhodonite

Rhodonite

Overview All minerals have crystalline structure; either on the

inside or outside With plenty of room they form on the outside If confined the crystals are in the atomic structure

Crystal size is dependent on how quickly (small crystals) or slowly (large crystals) they form

Crystals can form from magma or from solution There are 6 basic crystal shapes 5 of these are versions of cubes, the 6th is a hexagon All minerals are composed of crystals. Minerals are

“naturally occurring, inorganic solids with definite chemical composition and orderly arrangement of atoms.”