Mineral Lab B

GLS100Lab6: Mineral Identification
Physical Geology - Dr. Lindley Hanson

The goal of this lab is to systematically analyze and identify important economic and rock forming minerals. 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.
  • Draw recognizable illustrations of mineral specimens.
  • Properly identify minerals based on physical properties.
  • Identify the most common occurrence of minerals.
  • Identify the significance of a mineral as having economic value or by being an important component of rocks.

Procedure

You will be given a mineral identification form and assigned several specimens to identify. For each specimen:

1. Determine and record the physical properties.

2. Identify the mineral using the key provided.

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. Identifyhardness:

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 to test hardness wipe the powder offthe plate before noting a scratch. Also, make sure the edge of the specimen that 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 off of multiple crystals massive granular aggregates typically display a different luster than individual crystals.

4. Color

Note ALL colors observed in the mineral samples.

5.Test for the streak if the mineral is metallic, pearly, dull or waxy. If the mineral is
vitreous skip it.

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). If the mineral appears hard and the streak-powder is white, look for a scratch on the streak plate.

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 crystallineaggregates (e.g. graphite, olivine, chlorite, hematite, kaolinite, and talc) may not be visible. In such cases observable surface breaksare 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. Draw the sample (when requested*)

Drawing requires a greater understand of the properties. Your illustrations should show:

  1. How the shape reflects any pattern of cleavage or fracture.
  2. Whether it’s a single crystal, composite or aggregate.
  3. Colorand luster
  4. Any other visible characteristics

8. Look for and add any other properties:

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

9.Lastly, use the KEY in figure 1 to identify the mineral and the list below to indicate the
rock type the mineral is associated with.

Most common occurrence and economic significance of minerals

Rock Forming Minerals (Silicates):

Olivine I
Pyroxene (augite) I
Amphibole (hornblende) I
Micas (muscovite, biotite, chlorite) I/M$
Felspars (orthoclase, plagioclase) I/M$
Quartz I/M/S $
Clay (kaolinite) S $
Talc M $

Non-Silicates

Graphite M/$
Galena $
Gypsum S $
Hematite S $
Magnetite I $
Halite S $
Calcite S $

I/M/S Rock Forming Minerals (igneous / metamorphic / sedimentary)
$ Economically important mineral

Notes:

Figure 1. Key to the Classification of Mineral

1