1. Crystals

2. 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.

4. 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

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

6. Crystal Size
The 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

7. Crystals from Solution
Another way we can get crystals is from a solution
Remember, a solution is a mixture of two or more things that are not chemically combined
Sea water is a solution
When the water evaporated, crystals are left behind.

8. Cubic Crystals

9. Cubic Crystals
Cubic crystals have all 90 degree angles with all sides of equal length

10. Examples of cubic crystals
Galena

11. Cubic Crystals
Halite

12. Halite

13. 6-sided crystal
Sturmanite
Hexagonal Crystal

14. Hexagonal Crystals
Quartz

15. Tetragonal Crystals
Much like the cubic, except one side is longer than the others, like a rectangle.
Zircon is a good example

16. 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.

17. Orthorhombic has all 90° angles still
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.

18. Monoclinic
Take 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

19. Monoclinic crystal: Orthoclase

20. Triclinic This is an unsymmetrical as a mineral can get No 90°angles
Rhodonite is an example

21. More rhodonite

22. Rhodonite

23. 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.”