Mineral Identification Lab

 

You will be given nine sets of minerals that contain two different samples.  Use the physical properties of the unknown samples to identify the mineral.  Perform the following observations and tests and record any findings on your data sheet:  Color, luster, streak, hardness, cleavage/fracture, and any other properties you have identified.  Then answer the questions at the end of the lab.

 

Sample Number	Color	Luster	Hardness	Streak (note the color)	Cleavage/ Fracture	Other	Name of Mineral
1-A
1-B
2-A
2-B
3-A
3-B
4-A
4-B
5-A
5-B
6-A
6-B
7-A
7-B
8-A
8-B
9-A
9-B

 

 

 

Analysis and Conclusion:

 

Answer the following questions in full and complete sentences.

 

 

1.      Describe the properties that helped you identify each sample.

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2.      Although color is the most obvious property of a mineral, it is difficult to identify a mineral by its color alone.  Explain why this is so.

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3.      What is the difference between a scratch test and a streak test?

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

4.      Why do some minerals leave no streak?

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

5.      What is the difference between transparent, translucent, and opaque?

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

 

 

 

Hardness:  Based on Mohs Table of Hardness

 

Scratching tools:  Fingernail (2.2)  Copper Penny (3.5)  Piece of Glass (5.5)

 

Rating	Description	Example
1  SOFT	Easily crumbles.	Talc
2	Can be scratched with a fingernail  (2.2)	Gypsum
3	Can be scratched with a copper penny (3.5)	Calcite
4	Can be scratched with a pocket knife (4.2)	Fluorite
5	Can be scratched with a piece of glass (5.5)	Apatite
6	Minerals of 6 or more will scratch glass.	Feldspar
7	Can be scratched with a steel file (7.5)	Quartz
8		Topaz
9		Corundum
10 HARD		Diamond

 

Notes for testing:

 

1. Each mineral can scratch the minerals with lower hardness ratings.
2. Each mineral can scratch itself.
3. Don’t press hard – normal scratching will do.
4. Weathered surfaces are softer.
5. Corners or edges of crystals are softer.
6. Small pieces seem softer than large pieces.

 

Luster Vocabulary – Words used to describe the way light reflects off of                                   the surface of a mineral.

 

Word	Description
dull/earthy	no shine at all, may rub off on your fingers
greasy/oily	leaves a silky residue on your fingers
glassy/vitreous	looks like glass
submetallic	silvery or metallic luster, but mineral is transparent or translucent when in small slivers
metallic	highly reflective, opaque minerals

 

Cleavage -To break along flat surfaces.   Examples of Cleavage:

• Cubic- To break into cubes

     

• Rhombihedral- to break into “pushed over cubes”

 

• Basal- to split into thin sheets

           

Fracture -The way a mineral without cleavage breaks.

Examples of Fracture

• conchoidal- to break in a scooped out bowl shape- like a conch (sea snail)
• hackly fracture- to have irregular sharp edges
• splintery- to break into long, thin needles

Miscellaneous Tests

• Acid- Calcite and powdered dolomite will effervesce (fizz) in dilute hydrochloric acid (HCl)
• Smell- Sphalerite will give off a rotten-egg smell when streaked on a streak plate.
• Magnetism- Magnetite will pick up paper clips (weak samples will only be able to pick up staples)
• Taste- Halite is rock salt and will taste salty.
• Fluorescence- some minerals (mostly forms of calcite) will glow in fluorescent colors under a black (UV) light.
• Double refraction- some clear forms of calcite (Iceland Spar) will make a double image of words.