Mineral Websites

   Amethyst Galleries

             The University Corporation of                The Mineral and           

     Atmospheric Research Science website        Location Database

Identifying Minerals

Listed are the main defining characters used in identifying minerals

1. Color                                    3. Streak                            5.Form                               7.Other (Taste, Acid

2. Hardness                               4. Luster                            6. Specific Gravity                        Reaction, etc.)

1. Color

Primarily the most useless way of identifying minerals although the principle reason people love them.

Often several minerals contain the same color

Purple Minerals

Or the same mineral has several different colors

Quartz

Pictures used from and copyrighted from The Amethyst Galleries

2. Hardness

• Hardness is not determined by a hammer.

• Hardness in a mineral is the minerals resistance to scratching.

• Hence a diamond is so valuable because it can only be scratched by another diamond

• The hardness scale (Moh's Scale) runs from 1 (easiest to scratch) to 10 (hardest to scratch)

• Certain tools that have specific hardness's are used to determine the hardness range of an unknown mineral (Right column)

• Click on the mineral for a more in-depth description

Moh's Hardness Scale

Minerals                                         Tools              

Softest (Easiest to scratch)

1 - Talc                

2 - Gypsum

2.5 - Fingernail        

3 - Calcite

3.5 - Copper Penny

4 - Fluorite

4.5 - Steel Nail        

5 - Apatite

5.5 - Glass Plate      

6 - Orthoclase                       

6 - Ceramic Tile     

7 - Quartz

8 - Topaz

9 - Corundum

10 - Diamond 

Hardest (most difficult to scratch)

• To determine a mineral's hardness range using the tools attempt to scratch it with your fingernail first

• If it is not scratched move on to the penny

• If it is scratched by the penny then the hardness range is 2.5 (not scratched by fingernail) to 3.5 (scratched by penny)  [2.5-3.5]

• Repeat for any mineral

3. Streak

• Streak is the color of a powdered mineral

• Unlike color this is actually a very useful determination of a mineral sometimes

• Also unlike color this does not vary between samples, a mineral's streak is always the same.

• Determined by using a ceramic tile (#6 on hardness) and scratching the mineral across it. If it leaves behind a colored line, that is the streak.

• Streaks that are white or colorless are not very helpful in mineral identification

          Streak                                       Example of the color of a mineral

                                                                does not effect the streak

Two samples of Hematite, one silver (left) one red (right).

Both will give a characteristic bright red streak.  

Streak picture taken from ConodontGuy.com. Silver hematite picture take from the Windows by UCAR. Red hematite picture taken from a Student page at Washington University. Hematite streak picture taken from LSU.edu geo dept.     

4. Luster

• Luster is the way a mineral reflects light.

• There are 2 main types of Luster

Metallic

 - Looks like metal   

For Example - if it looks like a ring it is probably metallic

Nonmetallic

- Does not look like metal

- Can be broken into several different categories

- The most important category is that it is a nonmetal, the subcategories are not usually used

Categories    

         Pearly                         Glassy (Vitreous)

Dull                                   Waxy

    Earthy                                 Greasy

Pictures from JamesAvery.com, GeJem.com, and mindat.org. The pictures and links on this website are by no mean an endorsement for the jeweler or the products featured. The images are just used to illustrate a point.

5. Cleavage

• Cleavage is the way a mineral breaks along predefined planes (Not what most of you think)

• A mineral's cleavage is characterized by several methods

  • Whether is breaks into those planes at all (many minerals don't)

  • If it does - How many parallel planes they can break into (1-6, 1-3 are the most common)

  • And at what angle the plane intersect at - Used with 2 or 3 planes

• Note- Some minerals that don't break into cleavage planes have crystals which are a result of the way a minerals grows and not how it breaks

  • If you are to break a crystal is would not break parallel to the other crystal surfaces (hence not a cleavage face)

• A cleavage face is noticeable by the presence of a reflective surface (one side that reflects light uniformly)

     No Cleavage                              Conchoidal Fracture

   Breaks into just a random mess                      Shatters similar to glass

                                                                     with curved sharp pieces

Cleavage

     1 direction                                                  2 directions

                                                    sides @ 90^o               sides not @ 90^o

      Breaks into thin sheets        Elongated box with broken ends   Crushed box with broken ends

3 directions

sides @ 90^o                                    sides not @ 90^o     

Conchoidal fracture picture taken from Pinkrabbitsays. Hematite picture taken from a Student page at Washington University.

7. Other

• There are a variety of other tests that sometimes serve as ideal identification methods for some minerals. These include:

  • Magnetism

  

  • Reaction to acid (HCl)

  

  • Taste (salty or bitter)

  

          Salt                   Mineral Halite

  • Striations (Parallel lines on cleavage faces)

  

Magnetism picture from www.minerals.net. Acid and salt pictures from Conodontguy.com. Striations picture from The Amethyst Galleries

6. Specific Gravity

• Specific gravity (SG) is how dense an object is, or more simply how much an object weighs compared with another object of the same size.

• The least practical of the mineral tests

• Not commonly used unless in intensive tests or the result is blatantly obvious

  • Ex - Take a hollow plastic ball and compare the weight with a rock of the same size. They are both the same size but the ball weighs far less - hence has a lower SG

• Usually tested by placing minerals in a tube filled with water  ( a graduated cylinder as seen on the right) and seeing how much water they displace.