General Geology Lab 2: Identification of Minerals
I.
II.
III.
IV.
Introduction to Mineral Properties and Identification
Remember the definition of a mineral from lab 1: naturally occurring,
inorganic, solid element or compound with a regular internal structure and
fairly constant chemical composition
Nearly 4000 kinds of minerals are known, but the most important rockforming minerals are:
1. Feldspars
2. Quartz
3. Augite
4. Hornblende
5. Olivine
6. Micas
7. Iron Oxides
8. Calcite
9. Dolomite
10. Chlorite
11. Halite
12. Clays
Chemical Composition
Elements and ratios for specific minerals are fairly constant and are the
mineral’s “chemical fingerprint.” Example—Halite, NaCl; Quartz, SiO2
Internal Structure
The way atoms are arranged in the crystal structure of a mineral. All
specimens of the mineral will be structured in this specific way, regardless
of origin. Example—Halite, with cubic framework; Calcite, with
rhombohedral framework
Physical Properties
Luster—appearance of a mineral in reflected light. Metallic, non-metallic;
non-metallic usually described as vitreous or resinous
Hardness—resistance of a mineral to scratching.
Relative hardness scale developed in 1824 by Austrian mineralogist
Friedrich Mohs:
1. Talc (soft)
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Potassium Feldspar
7. Quartz
8. Topaz
9. Corundum
10. Diamond (hard)
Unfortunately, not all of these minerals are always available to us…
…so common available materials with known hardnesses are used:
1. Fingernail – Hardness 2.2
2. New Penny – Hardness 3.2
3. Nail – Hardness 5.0
4. Glass – Hardness 5.5
5. Streak Plate – Hardness 7.0
Streak—color of the ground-up or powdered mineral. Determined by
scratching specimen on an unglazed porcelain streak plate and observing the
color of the powder. Streak is usually more constant for a mineral than its
color in hand specimen, because grain size affects color.
Color—should be considered in mineral identification but not used as a
major identifying characteristic because of the variation in color from
specimen to specimen of some minerals
Reaction to Acid—some minerals effervesce when dilute HCl is applied to
their surface—carbonate minerals, some sulfates
Cleavage and Fracture—refer to the way a mineral breaks. Certain
minerals break along planes of weakness because of their internal structure,
leaving a smooth, strongly reflective surface or surfaces. This is known as
cleavage. Some have one plane of weakness, some two non-parallel planes,
some three; each mineral has its own particular cleavage. Note: crystal faces
should not be confused with cleavage planes. Example: Quartz has no
cleavage but can form nice crystal faces.
Minerals without cleavage break irregularly, and this is termed fracture.
Quartz breaks with conchoidal fracture, like glass.
Striations and thread-like markings—may be present on cleavage surfaces
of some minerals. Striations—plagioclase feldspar; thread-like markings—
potassium feldspar
V.
Identification of Minerals
1. Determine luster
2. Determine hardness
3. Determine cleavage
4. Determine color
5. Test for acid reaction
6. Other properties: striations, specific gravity, magnetism, taste, etc.
VI.
Chemical Symbols and Mineral Composition
Al—Aluminum
K—Potassium
C—Carbon
Mg—Magnesium
Ca—Calcium
Na—Sodium
See others in lab manual
VII. Important uses of some Minerals
See lab manual, page 14
VIII. Mineral Exercise I—minerals without cleavage
Study Chapters One and Two for Quiz Next Week!!!!!!