2. What Makes Something a Mineral?
In order for something to be considered a mineral it must meet some basic requirements.
All minerals are solid.
Something must be naturally formed to be considered a mineral. Diamonds made in a laboratory are very similar to diamonds made in nature, however they aren’t considered minerals.
When minerals begin to solidify, the atoms arrange themselves in a repeating pattern creating geometric shapes, as seen in Figure 1.
Solids with these types of atomic structures are called crystals.
Something must also be inorganic to be considered a mineral. Inorganic means that it wasn’t alive, nor did it come from anything that was once living. For example, sugar is considered organic because it is made by plants (Figure 2).
Figure 1. Atomic structure of halite (table salt) on the left shows the chlorine atoms (green) and the sodium atoms (blue) bonded together in a cubic crystalline shape. On the right is a sample of halite, which is also showing cubic crystals.
Figure 2. The sample of sugar above is solid, is formed in nature, has a crystalline structure, but because it is made through biological processes it isn’t considered a mineral.

3. Crystal Growth
The video above shows super-cooled water. A single crystal is dropped into this super-cooled water and acts as a nucleation site from which other crystals grow. Pay close attention to how the crystals all have the same geometric shape, which is a result of the atoms bonding to each other in a repeating pattern.

4. Mineral Formation Minerals form in two primary methods.
When molten rock (Figure 3), such as magma or lava, cools it will eventually reach a temperature at which it begins to solidify. When this happens the atoms in the molten rock begin bonding to each other many different solids which are minerals (Figure 4).
Figure 3. Lava that has erupted from a Hawaiian volcano and is beginning to solidify.
2 different minerals
Figure 4. This sample of granite is formed from magma that slowly cools several miles beneath the surface of Earth. Notice the different minerals that make up this rock.

5. Mineral Formation
2. The second primary way in which a mineral can form is from the precipitation of a solution.
Some minerals can be dissolved in water forming a solution (Figure 5).
When the solution can no longer hold any more of the dissolved minerals it is said to saturated and the minerals will begin to come out of the solution in a process called precipitation (Figure 6).
There are several ways that a solution can become saturated.
There is a direct relationship between the temperature of a solution and the amount of dissolved material it can hold. Therefore as the temperature drops the solution can’t hold as much dissolved materials and precipitation will occur. (The same thing occurs in air. When the temperature drops, the air can no longer hold the moisture in the air and condensation occurs.)
If a solution begins to evaporate the ratio of water to dissolved material changes and the solution becomes more concentrated. This can also cause the solution to reach its saturation point.
Figure 5. A solution of salt water.

6. Figure 6. This mineral gypsum formed from the precipitation of sea water in Australia. The green color is a result of impurities in the mineral.

7. The next 5 slides are all pictures of gypsum crystals that have formed from the precipitation of sea water. They grew in the a series of caves located in Mexico and is sometimes called Crystal Cave of Giants.

12. Mineral Groups
Minerals are put into groups based on their composition (what elements make up the mineral).
The most common types of minerals are called the silicates because they are made of the two most abundant elements on earth, silicon and oxygen (Figure 7).
Figure 7. Found on the cover of the E.S.R.T., this table shows that the two most common elements that make up Earth’s crust are oxygen and silicon.

13. Unique Minerals
An ore is a mineral that has value because it is used for industrial purposes. Usually minerals that contain metals are considered ores (Figure 8).
A gem is a mineral that has value because of its rarity and/or beauty (Figure 9). a b
Figure 8. Hematite (a) and bauxite (b) are minerals that are mined for their iron and aluminum respectively.
Figure 9. The ruby (red) and sapphire (blue) gemstones seen above are varieties of the same mineral, corundum. The emerald is a mineral called beryl.

14. Ways to Indentify Minerals
The first and most obvious way to identity a mineral is based on it’s color (Figure 10). Although the color may be the easiest and most obvious property of a mineral, it is the least reliable method.
Figure 10. The mineral above is sulfur. Unlike many minerals, sulfur can be easily identified by its very bright yellow color.

15. Ways to Identify Minerals – Color
Color is the least reliable property used to identify a mineral for a couple of reasons.
One reason is that two different minerals can be the same color, as seen in Figure 11.
The second reason is due to impurities in a mineral, one mineral can come in a variety of colors.
Figure 10. The mineral above is sulfur. Unlike many minerals, sulfur can be easily identified by its very bright yellow color.
Figure 11. All of the samples seen above are the same mineral, quartz.

16. Ways to Identify Minerals - Luster
Another way to identify a mineral is based on how the light reflects off of the mineral. This physical property is known as luster.
There are two different lusters that you are responsible for determining. If the mineral looks like a metal it is said to have a metallic luster. If it doesn’t it is said to have a non-metallic luster.
Figure 12 shows the two different types of luster.
Potassium Feldspar
Figure 12. The sample of feldspar has a non-metallic luster while the samples of pyrite (gold color) and the galena (silver color) but look like metals and therefore have a metallic luster.

17. Ways to Identify Minerals – Streak Test
A minerals streak is the color that a mineral leaves behind when rubbed against something, usually an unglazed porcelain plate (Figure 13).
Figure 13. The picture above demonstrates a streak test.

18. Ways to Identify Minerals – Streak Test
The streak test is a more reliable identification test because, as seen in Figure 14, two minerals with the same color could produce a different streak. Also although a mineral’s color could vary its streak color usually remains constant.
Figure 14. The sample on the top is gold, while the sample below is pyrite. Notice both have the same color, however they produce different streaks. This is one way to differentiate gold from pyrite.

19. Ways to Identify Minerals – Breakage
There are two ways in which a mineral can break. Cleavage is when minerals break along planes of weakness. This occurs because the atomic bonds along certain planes can be weak and therefore when pressure is applied the mineral tends to break along that weakness (Figure 15).
Figure 15. On the left is a diagram showing some of the different cleavage planes that can exist in different minerals. On the right are the actual samples of those minerals.

20. Calcite Showing Cleavage
This video shows that when pressure is applied, minerals displaying the property of cleavage tend to break along the planes of weakness. In this case, because calcite has rhombohedral cleavage, when smashed with a hammer the pieces that break off are mostly rhombuses.

21. Ways to Identify Minerals – Breakage
The other way a mineral can break is called facture. Fracture is when minerals break randomly. Like cleavage, this is related to the atomic structure of a mineral. If the atomic bonds that hold the atoms together are not weaker or stronger in any one direction the mineral, like a piece of glass will break randomly (Figure 16).
Figure 16. Above are several different minerals that all share the same physical property of fracture.

22. Ways to Identify Minerals – Hardness
A very useful physical property to test is a minerals hardness. A mineral hardness refers to its resistance to being scratched.
To do this you use the Mohs Hardness Scale which ranks minerals on a scale from This scale has been established by scratching minerals against objects with a known hardness. Talc is the softest mineral on earth and has a hardness of 1, while diamond is the hardest mineral on Earth and has a hardness of 10.

23. Atomic Structure
The physical and chemical properties of a mineral, such as hardness, crystal shape, color, type of breakage, etc. is determined by the atomic structure.

24. Special Properties
Acid Test

25. Magnetic