Minerals and their usage

Internet exercise

Dr. Anna Balog-Szabo

 

To define minerals we use their Physical Properties in the field or the lab. The following list shows the known and used properties.

Color

Streak

Luster

Hardness

Cleavage or Fracture

Crystalline Structure

Magnetism

Reaction with hydrochloric acid

 

1.     Color

Minerals usually have a distinctive color that can be used for identification.

Translucent to transparent minerals however have a varied degree of color due to the presence of trace minerals (Exotic coloration). Therefore, color alone is not reliable as a single identifying characteristic.

In opaque minerals, the color tends to be more consistent, so learning the colors associated with these minerals can be very helpful in identification.

Use your favorite search engine to learn about the exotic coloration of minerals, collect thumbnail pictures and names of examples of the same mineral with different color. And tell me what trace element causes the color?

Find at least three minerals with varying coloration, and at least three colors for each and their names also figure out the cause of the color?

 

 

 

 

 

 

 

 

2.   Streak

Streak is the color of the mineral in powdered form. Streak shows the true color of the mineral. In large solid form, trace minerals can change the color appearance of a mineral by reflecting the light in a certain way. Trace minerals have little influence on the reflection of the small powdery particles of the streak. The streak of metallic minerals tends to appear dark because the small particles of the streak absorb the light hitting them. Non-metallic particles tend to reflect most of the light so they appear lighter in color or almost white.

Because streak is a more accurate illustration of the mineralís color, streak is a more reliable property of minerals than color for identification.

What tool do we use to define the streak of the mineral?

 

Please use your search engine to find 5 different minerals with characteristic streak color. Collect a thumbnail picture for each!

 

 

 

 

 

 

 

 

 

 

3.     Luster

Luster is the property of minerals that indicates how much the surface of a mineral reflects light. The luster of a mineral is affected by the brilliance of the light used to observe the mineral surface. Luster of a mineral is described in the following terms: Metallic The mineral is opaque and reflects light as a metal would. Submettalic The mineral is opaque and dull. The mineral is dark colored. Nonmettalic: The mineral does not reflect light like a metal. Nonmetallic minerals are described using modifiers that refer to commonly known qualities. Here is a list you can use:

adamantine: brilliant, e.g. diamond

vitreous: glassy

resinous: appearance similar to resins or saps of certain trees or shrubs

greasy: like oil on glass

pearly: pearl

silky: like silk, usually fibrous textures

earthy: like dirt

 

Please collect thumbnail pictures for each type of luster with name.

 

 

 

            

 

 

 

 

 

 

 

 

 

 

 

 

4.     Hardness

Hardness is one of the better properties of minerals to use for identifying a mineral. Hardness is a measure of the mineralís resistance to scratching. The Mohs scale is a set of 10 minerals whose hardness is known. The softest mineral, talc, has a Mohs scale rating of one. Diamond is the hardest mineral and has a rating of ten. Softer minerals can be scratched by harder minerals because the forces that hold the crystals together are weaker and can be broken by the harder mineral.

The following is a listing of the minerals of the Mohs scale and their rating:

  1. Talc
  2. Gypsum
  3. Calcite
  4. Fluorite
  5. Apatite
  6. Orthoclase Feldspar
  7. Quartz
  8. Topaz
  9. Corundum
  10. Diamond

Use your favorite search engine what kind of easy tools can we use to identify the hardness of the different minerals?

Find the hardness of the following minerals:

k-feldspar:

garnet:

muscovite:

graphite

ruby

topaz

aquamarine

 

 

5.     Cleavage/fracture

Minerals tend to break along lines or smooth surfaces when hit sharply. Different minerals break in different ways showing different types of cleavage.

Cleavage is defined using two sets of criteria. The first set of criteria describes how easily the cleavage is obtained. Cleavage is considered perfect if it is easily obtained and the cleavage planes are easily distinguished. It is considered good if the cleavage is produced with some difficulty but has obvious cleavage planes. Finally it is considered imperfect if cleavage is obtained with difficulty and some of the planes are difficult to distinguish.

The second set of criteria is the direction of the cleavage surfaces. The names correspond to the shape formed by the cleavage surfaces and are defined specifically by the angles of the cleavage lines as indicated in the chart below:

Please collect thumbnail pictures and names of minerals with the given type of cleavages

Cubic Cleavage:

 

Rhombohedral cleavage:

 

Octahedral Cleavage:

 

Basal Cleavage:

 

Prismatic cleavage:  

 

 

Fracture describes the quality of the mineralís broken surface. Most minerals display either uneven or grainy fracture, conchoidal (curved, shell-like lines) fracture, or hackly (rough, jagged) fracture.

Please collect a thumbnail picture and the name of the mineral with each type of fracture.

 

 

 

 

 

 

 

6.     Crystalline Structure

Minerals occur in various shapes and sizes. The particular shape is determined by the arrangement of the atoms, molecules or ions that make up the crystal and how they are joined. This is called the crystal lattice. If there is no crystalline structure, it is called amorphous. However, there are very few amorphous crystals and these are only observed under extremely high magnification.

We classify crystals into six different systems based on symmetry. To do this without the aid of an optical microscope or x-rays, the mineral must have grown with crystal faces present. The planar surfaces resulting from crystal growth may be distinguished with care from cleavage surfaces by the presence of impurities, growth striations, or tarnish (lack of fresh look) upon the growth surface. Since crystal faces are a reflection of an orderly internal atomic arrangement, there is a possibility that the planes they represent are also planes of weakness and cleavage.

 

Please collect thumbnail pictures of at least 5 different minerals typical crystal forms.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7.     Magnetism

Magnetic susceptibility

Diamagnetic minerals- minerals not attracted by a magnet.

Paramagnetic minerals - minerals attracted by a magnet.

Please find thumbnail picture and name for minerals which are paramagnetic. Why would a mineral be paramagnetic?

 

 

 

 

 

8.     Reaction with hydro-chloric acid

Certain minerals will effervesce (bubble) when dilute hydrochloric acid is applied to the surface. This is characteristic of those minerals containing the carbonate anion

CaCO3 + 2HCl = CaCl2 + H2O + CO2 (gas).

The amount of effervescence depends upon how soluble the mineral is (calcite vs. dolomite)

Please figure out which mineral will effervesce the most and least?

 

 

 

 

 

 

 

Minerals and how do we use them

Use the following internet site: http://geology.com/minerals/ and collect thumbnail pictures and information (color, hardness, cleavage, luster, streak) about the following minerals (Best is if you make up a table by hand) :

1.      Quartz

2.      Chert

3.      K-feldspar

4.      Ca-Plagioclas

5.      Na-Plagioclase6

6.      Olivine

7.      Pyroxene

8.      Amphibole

9.      Biotite

10.  Muscovite

11.  Kaolinite

12.   Talk

13. Garnet

14. Calcite

15. Dolomite

16. Halite

17. Gypsum

18. Magnetite

19. Fluorite

20. Galena

21. Pyrite

22. Hematite

23. Graphite

24. Bauxite