Mineral Identification Lab

 

Objective: 

Use what you know about the physical characteristics of minerals to be able to identify an unknown mineral.

 

Background Information:

A mineral is... a naturally occurring, inorganic, crystalline solid.

How do we identify minerals?  Physical Characteristics such as...

 

 

Color

Variations in color of the same mineral

Although color is the most obvious, it is the least reliable. Often the same mineral can be found in a wide range of colors. The above picture contains only the mineral calcite. Other minerals like pyrite will always show the same color.

 

Hardness: Mohís Scale

To determine hardness refer to Mohís hardness scale. If the item can be scratched by another item it is softer than the item that was able to scratch it. If that item cannot scratch it then it must be softer. If we have a sample that we can scratch with Fluorite, but not with Gypsum, we can predict that the samples hardness is around 3.  A simple field method is rather similar. All you do is try to scratch the unknown mineral with various items, such as a fingernail (hardness of about 2.5), a penny (3), a steel nail (5.5) and a steel file (7). The item that first scratches the unknown is harder than the unknown so now you must estimate. Below is the Mohs Scale.  


Table 7.2 Mohs' Hardness scale (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).

 

Streak

When an unknown mineral is rubbed against a piece of unglazed porcelain ( aka-streak plate) it may produce a colored line. This color will help to determine the minerals identification. If the sample does not leave a streak then it is harder than the streak plate.

 

Fracture and Cleavage

These terms describe the way a mineral breaks. If a mineral fractures, it breaks along rough edges. If it cleaves, then it breaks along smooth, flat surfaces. Notice the illustration, this Biotite cleaves into flat sheets on the top, but it fractures on the sides.

 

Luster

 The way a mineral reflects light is itís luster. Does your mineral appear to be a metal (metallic luster)? Or does it look like a nonmetal (nonmetallic luster)? There are several other words used to describe luster, but for our purposes only state if it has a metallic (metal like) or non metallic. (not metal like luster)

 

 

Many items may display special properties such as being magnetic, or they may react to acid. Other minerals may dissolve in water, or have a salty taste.

 

 

Steps To FOLLOW:

  1. At each lab station, you will need to identify the physical characteristics of your unknown mineral...

    1. Use information above to define the: color, hardness, streak, fracture/cleavage, and luster of the mineral... record this in the data section (# should match container #).

    2. Another identifying characteristic is a reaction to hydrochloric acid... so drop ONE drop of the diluted HCl on each mineral to check for fizzing.

    3. Yet another identifying characteristic is magnetism... so use the magnets to see if the mineral displays magnetic characteristics.

  2. ONLY after you have gone to each station, compare your sheet of characteristics to the characteristics for the known minerals (click here).  You should be able to identify what each mineral is using that resource.

  3. Label what each mineral is in the Results section.

 

Writing the Conclusion:

 

The conclusion ALWAYS relates back to the objective of the lab.  Thus, you need to state if and how you met the objective.  For instance, "I identified the unknown minerals in this lab."  You should also ALWAYS include the results of meeting the objective.  For instance, "I identified the unknown minerals in this lab.  Mineral #1 was _________... mineral #2 was ________... etc..."  Lastly, you need to describe in two or more sentences HOW you were able to identify the unknown minerals.  Be general about how you identified... don't list every single step you did.

 

Lab Write up Sheet