Mineral Lab part 2

GLS100 Lab - Mineral Identification
Physical Geology - Dr. Lindley Hanson

The scientific method is systematic and methodical. Conclusions are based on facts, not subjective analyses. The goal of this lab is to apply the scientific method to the identification of minerals using their physical properties. To achieve this goal you will apply the mineral properties learned in the previous lab.

Objectives

  • Accurately determine mineral fracture and cleavage.
  • Accurately determine hardness within the range of your fingernail and glass plate.
  • Distinguish between metallic and non-metallic luster.
  • Identify luster, elasticity, brittle behavior, double refraction, and other physical properties.
  • Properly identify minerals using their physical properties.
  • Learn which minerals are of economic importance.
  • Learn the important rock-forming minerals.
  • Associate minerals with the type of rock in which they are most commonly found.

Procedure

You will be given three blank tables with several assigned specimens to identify. For each specimen:

1. Determine and record the physical properties. Always move from left to right when filling the table.

2. Identify the mineral using the key on page 4.

3. Check to make sure that the specimen you have fits all of the properties described.

INSTRUCTIONS AND HELPFUL HINTS for filling out the form and identifying the minerals:

1. Be systematic

Lab sciences teach a systematic approach to problem solving. Do not guess at the minerals. Be systematic in obtaining and applying the facts.

2. Identify hardness:

Using a glass plate and your fingernail determine the range (<2.5; 2.5<5.5>5.5; >5.5) of hardness the mineral falls into. (“>” means greater than, “<” means less than. Don’t confuse these symbols!)
Technique: When using a glass plate wipe the powder off the plate before noting a scratch. Also, be sure the edge of the specimen your testing is solid and unbroken otherwise the mineral will break off along micro-fractures and appear softer than it is.

3. Identifying Luster:

If the luster is non-metallic then note whether it’s vitreous, pearly, waxy, dull or greasy. Some minerals exhibit more than one luster.

Note: Luster is best observed on a freshly fractured or cleaved surface. Minerals described having a vitreous luster may appear dull, waxy or pearly if weathered or extensive handling. Because of the dispersion of light reflecting off multiple crystal surfaces minerals that typically occur as granular aggregates will display a different luster than the individual crystals.

4. Color

Record ALL colors observed in the mineral samples. Minerals that tend towards transparency common exhibit more that one color.

5. Test for the streak if the mineral is metallic, pearly, dull or waxy. If the mineral is
vitreous skip it will either have a white streak (if <5.5) or no streak (if >6).

Streak is the color of the crushed mineral. It only needs to be determined from one specimen.

If the mineral is flexible (e.g. muscovite), or harder than 6 (e.g. corundum) it will not produce a streak (powder).

6. Breakage

Determine if the mineral cleaves. If so then identify the cleavage. If not then identify the fracture. Don’t bother identifying the fracture of a mineral that cleaves.

For some of the minerals that have 2 or 3 directions of cleavage, one direction may be much more prominent than the others (examples: gypsum and feldspar).
Cleavage is best identified on single, large (>1 cm) broken crystals. Mineral breakage in crystalline aggregates (e.g. graphite, olivine, chlorite, hematite, kaolinite, and talc) may not be visible. In such cases observable surface breaks are a function of how the rock fractures between individual crystals (parting), which may not relate to how the mineral grains break. Terms such as uneven, flaky, conchoidal, and fibrous apply.

7. Look for and add any other properties:

specific gravity, feel, diaphaneity, magnetism, taste, double refraction, and crystal form, and habit.

8. What if you can’t determine a property?

There will be times when you can’t identify certain properties, such as breakage and luster in granular aggregates. In such cases, look at the mineral under the microscope. If you still are uncertain then skip the property, put a “?” in the column, and used those properties that you are confident into identify the mineral.

Most common occurrence and economic significance of minerals

Rock Forming Minerals (Silicates):

Amphibole (hornblende) I
Chlorite M
Garnet M/I$
Felspars (orthoclase, plagioclase) I/M$
Kaolinite Clay S$
Micas (muscovite, biotite) M/I$
Olivine I
Pyroxene (augite) I
Quartz I/M/S $
Serpentine M
Talc M $

Non-Silicates

Chalcopyrite and Pyrite H$
Galena H$
Graphite M/$
Gypsum S $
Fluorite H$
Halite S $
Hematite S (bif) M (specular) $
Magnetite I $
Calcite S $

I/M/S Rock Forming Minerals (igneous / metamorphic / sedimentary)
H Occurs in hydrothermal veins, deposited by hot fluids migrating through rocks
$ Economically important mineral

Notes:

Figure 1. Key to the Classification of Mineral

What to study

A. For the quiz next week be able to identify the following basic rock-forming silicate minerals:

  • Augite (pyroxene)
  • Biotite mica
  • Hornblende (amphibole)
  • K-feldspar (orthoclase, microcline, potash feldspar)
  • Muscovite mica
  • Na-Plagioclase feldspar (albite)
  • Ca-Plagioclase feldspar (anorthite)
  • Quartz

Don’t be confused by group names.

Pyroxene, amphibole, feldspar, and mica are names for silicate mineral groups; minerals that have the same structure but vary slightly in composition. Within each group we are only interested in one or two minerals, for example biotite and muscovite (mica group), augite (pyroxene group) and orthoclase, albite and anorthite (feldspar group). Plagioclase is a subgroup of the felspars.

How to study

1. Best method: Come to the lab during your free time to study the minerals.

2. Second Best: Use the following websites to help you learn the minerals:

  • Mineral Systems and Physical Properties: http://facweb.bhc.edu/academics/science/harwoodr/geol101/study/minerals.htm
  • USGS Minerals Close Up: http://geomaps.wr.usgs.gov/parks/rxmin/mineral.html
  • Mineral Information Institute:

B. For the Midterm and Final lab exams you need to study all the minerals listed on page 3.

NOTES:

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