Geological Sciences 100

EARTH SYSTEM I:
GEOLOGICAL ENVIRONMENT

Lecture VII. Rock-Forming Minerals

A) Crustal Abundances of Minerals	B) Characterization of Minerals
C) Physical Properties of Minerals	D) Examples

A) Crustal Abundances of Minerals

Figure 7.1 Relative abundance of minerals in the earth's crust. Data from Ronov and Yaroshevsky, 1969 (from General Geology (5th ed.), by Foster, Merrill Publishing Co., 1988).

Table 7.1 Relative abundance of the most common elements in the earth's crust (from The Earth - An Introduction to Physical Geology (2nd ed.), by Tarbuck & Lutgens, Merrill Publishing Co., 1984).

B) Characterization of Minerals

Natural, inorganic elements or compounds having crystalline structure

Chemical compositions that are fixed or vary within fixed limits

single elements ==> Ag, Au, Cu, S, etc.

most are compounds in either

fixed composition ==> Si O2 (quartz) or

solid solution ==> (Fe, Mg)2 Si O4

Figure 7.2

Solids with internal structure ==> crystalline

Figure 7.3 Principle of X-ray diffraction. After Gilluley, Woodford, and Waters (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).

Figure 7.4 Halite structure showing models of internal arrangement (a) space lattice; (b) a packing diagram. (c) The external form of a visible crystal (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).

Figure 7.5 Silicon tetrahedron (a) Lattice diagram. (b) Packing diagram (silicon ion hidden in center). Representation of tetrahedron; points are at the nuclei of ions. (d) Chain structure, as in pyroxene, showing relation of (b) and (c). (e) Double chain, as in amphibole. (f) Sheet structure as in mica (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).

Solids that lack a regular arrangement of atoms and ions ==> mineraloids

Figure 7.6 Opal in limonite (Australia).
C) Physical Properties of Minerals
- crystal form
  
  Figure 7.8 Emerald crystals in limestone (Muzo, Columbia).
  
  Figure 7.9 Tiffany Diamond (Africa, 1871).
- luster ==> metallic, non-metallic, vitreous, pearly, silky, resinous, earthy, adamantine, etc.
  
  Figure 7.10 Calcite (Indiana).
  
  Figure 7.11 Pyrite (Elba, Italy).
- color
  
  Figure 7.12 Agate (Brazil).
  
  Figure 7.13 Rare moss agate with 'tree' (Ferus, Brazil).
- streak
- specific gravity ==> SG (qtz) = 2.67
  
  Figure 7.14 Quartz crystal group (Hot Springs, Arkansas).
  
  SG (galena) = 7.5;
  
  Figure 7.15 Galena, sphalernite, calcite (Kansas).
  
  SG (Au) = 20
  
  Figure 7.16 Large stream nugget of gold.
- hardness
  
  Table 7.2 Mohs' Hardness scale (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).
  
  Figure 7.17 Ruby (corundum) in green zoisite (Tanzania).
  
  Figure 7.18 Star of India Sapphire - 563 carets (Am. Museum of Nat. History, NY).
- cleavage/fracture
  
  Figure 7.19 Schematic representation of cleavage and the lack of it in certain minerals (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).>
D) Examples

Figure 7.20 Summary chart of general properties of some of the commonest rock-forming minerals (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).