1. Minerals Geology 101, Fall 2010

2. Mineral Definition: “A naturally-occurring homogenous inorganic solid substance with a definite chemical composition and a characteristic crystalline structure.” What about ice (frozen H 2 O)?

3. Mineral Definition: “A naturally-occurring homogenous inorganic solid substance with a definite chemical composition and a characteristic crystalline structure.” Ice does not have a “characteristic crystalline structure” -- thus it is a mineraloid.

4. Atomic theory John Dalton (1800): “Matter is made out of atoms -- the smallest units with distinguishable chemical properties.”

5. Molecules Atoms form associations called molecules; atoms in molecules are held together by chemical bonds

6. Crystals Molecules can attract each other due to intermolecular forces -- much weaker than chemical bonds If the molecules are held together in a regularly spaced lattice, a crystal is formed

7. Ice’s structure Note large-scale irregularities in the symmetry of the lattice -- ice is a mineraloid

8. Mineral intermolecular force Molecules in minerals are held together by ionic bonds -- the atoms lose or gain electrons and are thus called ions Positively charged ions are cations; negatively charged ions are anions

9. Geologists and minerals Minerals are the components of rocks Unlike minerals, rocks do not have a single definite chemical composition, and minerals retain their integrity when incorporated in a rock

10. Granite = rock

11. Mineral classification Basic classification is by chemical composition, typically by the anion it contains: Carbonates (CO 3 2– ) Halides (e.g., Cl – ) Phosphates (PO 4 3– ) Sulfates (SO 4 2– ) Oxides (O 2– ) Sulfides (S 2– )

12. Silicates But no mineral class is as prevalent as those made with the silicate anion (SiO 4 4– ) -- 95% by volume of the crust Tetrahedral shape

13. Silicate structure Since silicates are all the same shape, it is the arrangement of the silicates, and the cations that electrically balance the silicates that determine the structure of the mineral

14. Silicate structure Knowing the way the ions stack can tell you some mineral properties Sheet silicates (phyllosilicates) form thin sheets because there are not many ionic bonds between different levels of molecules

15. Silicate structure Tectosilicates (framework silicates) have a much more complex structure but have regular planes of weaker forces -- leads to characteristic 60°/120° cleavage of these minerals