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Mineral Identification

LESSON PURPOSE:   To conduct a series of tests in order to identify our minerals.

Scientists use a combination of the following tests when determining the identification of a mineral.

 

Luster: Is the way light is reflected from the mineral. A mineral’s luster is determined by the way in which its surface reflectslight.The two basic types of luster are metallic (having the opaque shininess characteristic of metals) and nonmetallic.  Nonmetallic lusters are further distinguished by the use of such terms as glassy, oily, silky, and dull.  Use the magnifier to look closely at the minerals surface.

 

 

 

 

 

 

 

Hardness or scratch test:  The mineral’s hardness is determined by testing to see whether a mineral scratches or is scratched by other materials.  If the mineral is scratched by your fingernail then it’s “approximate” hardness is 2.5 and so on (see the chart below).

Mohs’ Scale of Hardness
Fingernail                 1 – 2.4
Penny                       2.5 – 3.9
Nail or Steel Blade   4 – 5.4
Glass                        5.5 – 6.9
Will Scratch Glass    7 – 10

 

 

 

 

Streak:  Each mineral makes a powder streak of a certain color.  This color may be different than the color of the mineral itself because of weathering or impurities. To test for the streak, rub the mineral across a piece of white tile and then record the color of the powder that is left behind.

 

 

 

 

 

 

 

 

Hydrochloric Acid Test:  The acid test is useful for detecting the presence of calcite in a mineral.  If calcite is present, then the Hydrochloric acid (HCl) solution will cause a small amount of fizzing or bubbling.  To conduct this test, use a nail to scratch a small amount of powder from a specimen onto a glass plate.  Put a drop of the HCL acid solution on the powder and use a magnifier to observe any reaction.  Safety: you must wear goggles while performing this test!!

 

 

 

 

Cleavage or Fracture:  The way a mineral looks when it breaks can help determine its identity.  Certain minerals break with a clean edge known as cleavage.  Think of a butcher cutting meat with a meat cleaver that provides a nice straight cut.  Other minerals break with a rough jagged edge known as fracture.  Think of a broken arm where the bone breaks with rough and irregular edges.

 

 

 

 

 

 

SPECIAL PROPERTIES

Magnetic:  Test the mineral to see if the magnet is attracted or not.

Smell:  Smell the mineral and then use the following descriptions:  Earthy, Sour, Sweet, Rotten Egg, or No-

Smell

Feel:  Feel the mineral and then use the following descriptions:  Gritty-Sandy, Powdery-earthy or chalky, Smooth-Glassy, Smooth and Sticky-Waxy, and Sharp-Metallic.

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