Download Mineral

Chapter 2
Atoms, Elements, and Minerals
Minerals
• Mineralogy: study of minerals
• Mineral: naturally occurring, crystalline (solid),
inorganic substance that possesses a fairly definite
chemical composition and a distinctive set of physical
properties
– Most are composed of 8 elements (silicon, oxygen
compose 75% of the crust)
– Over 4500 are known
– 10 account for more than 90% of the crust
Atoms & Elements
Atoms: Smallest, electrically neutral assemblies of
energy & matter
Electrons: Negative charged particles that orbits
the nucleus
Nucleus: Core of the atom containing neutrons and
protons
Protons: Positive charged particles
Neutrons: Neutrally charged particles
Element: Defined by the number of protons
(atomic number)
Atomic Mass Number: Number of protons +
neutrons
Isotopes: Atoms containing different number of
neutrons (same number of protons)
Atomic Weight (Mass): Weight of an average atom
Helium and Neon Atoms
Fig. 2.6 Diagrammatic representation of
(A) sodium and
(B) chlorine ions
Bonding
Ionic Bonding: Electrons exchanged
Covalent Bonding: Electrons shared, e.g. Carbon & Silicon
Metallic Bonding: e.g. gold & iron, electrons free to move
throughout the crystal
Polymorphs: Different crystal structures with same chemical
composition
Fig.2-3 Model of the crytstalline
structure of the mineral natrolite
• Small spheres: Na
• Large spheres: H2O
• Pyramids: SiO4 tetrahedrons
Figure 2.10 (A) The silicon-oxygen tetrahedron
(B) The silicon-oxygen tetrahedron showing the corners
of the tetrahedron coinciding with the corners of
oxygen ions
• A SiO4 –4
Atomic framework for the most common minerals
B
Figure 2.12 Common silicate structures. Arrows indicate
directions in which structure repeats indefinitely
• Si2O7 –6
Figure 2.13 Diagram of the crystal structure of
olivine, as seen from one side of the crystal
Fig. 2.14 Single-chain Silicate Structure
• (A) Model of a singlechain silicate mineral
• (B) The same chain
silicate shown
diagrammatically as
linked tetrahedrons
Fig. 2.22 (B) Mica
• Sheet silicate
Silicates
• Quartz: SiO2, 3-D framework tetrahedra
• Feldspar: most abundant mineral in crust
– Plagioclase feldspar  O, Si, Al, and Ca or Na
– Potassium (orthoclase) feldspar  O, Si, Al, and K
•
•
•
•
•
Single independent tetrahedron  olivine
Single chain  pyroxene
Double chain  amphibole (e.g. hornblende)
Sheet  mica (e.g. muscovite & biotite)
3-D framework  quartz
Physical Properties of Minerals
(Identification of Minerals)
• Classified using physical & chemical properties –
usually, only physical properties are used
• 1. Crystal form: size & shape assumed by crystal faces when crystal has
time & space to grow
– External Crystal Form: set of faces that have a definite geometric
relationship to one another.
– Steno’s law: The angle between two adjacent faces in a mineral are
always the same.
• 2. Hardness: resistance to scratching
– Mohs’ hardness scale:
• Fingernail  2.5
• Penny  3
• Window glass or knife blade  5.5
• Steel file  6.5
Moh’s Hardness Scale
•
•
•
•
•
1.
2.
3.
4.
5.
talc
gypsum
calcite
fluorite
Apatite
•
•
•
•
•
6. orthoclase feldspar
7. quartz
8. topaz
9. corundum
10. diamond
Physical Properties
• 3. Cleavage: tendency to break along definite planes
• Fracture: way a mineral breaks
– Splinter
– Conchoidal fractures
• 4. Color: reflecting light, not a reliable property because of
impurities
• 5. Streak: color of powder of mineral
• 6. Luster: appearance of mineral’s surface in reflected light
– Metallic
– Nometallic
• Vitreous (glassy)
• Pearly
• Greasy
• Earthy/dull
Physical Properties
• 7. Specific gravity: ratio of mineral’s weight to an equal
volume of water
• 8. Taste: Not recommended
• 9. Double (refraction) imaging: e.g. calcite
• 10. Reaction to HCl: calcite & dolomite
– CaCO3 + 2HCl  CaCl2 + H2O + CO2 (g)
• 11. Magnetism:
• 12. Striations: Straight parallel line on flat surfaces, e.g.
plagioclase feldspar
Conditions of Mineral Formation
• Geological
– Precipitate from molten rock (magmas & lavas)
– Precipitate in ocean water
– Precipitate in springs, caves, lakes
– Precipitate due to evaporation
– Sublimation at volcanic vents from gases
• Biological
– Calcite in coral reefs
– Magnetite in skulls
– Sulfate minerals from bacteria