1. Sedimentology Grain Mineralogy Reading Assignment: Boggs, Chapter 5

2. Key Concepts Context of crust composition and surface rock composition
Quartz
Feldspar
Rock fragments
Other grains
Classification

3. Sedimentology Grain Mineralogy (1): Crustal composition Reading Assignment: Boggs, Chapter 5

4. Crust Composition: Elements
There are 92 naturally occurring elements, but most are rare.

5. Crust Composition: Minerals
Silicate Minerals
Common Silicate Minerals: Feldspar, Quartz, Olivine,
Pyroxene, Amphibole, Mica

6. Crust Composition: Minerals
Silicate Minerals
Common Silicate Minerals: Feldspar, Quartz, Olivine,
Pyroxene, Amphibole, Mica
Common Non-Silicate Minerals: Carbonates, Oxides,
Sulfides, Phosphates, Salts

7. Crust Composition: Minerals
Silicate Minerals
Common Silicate Minerals: Feldspar, Quartz, Olivine,
Pyroxene, Amphibole, Mica
Common Non-Silicate Minerals: Carbonates, Oxides,
Sulfides, Phosphates, Salts
There are ~ 3000 minerals
But 10 account for 90% of crust!

8. Crust Composition: Rock Type
Continental Crust:
Granite ~ 60% Feldspar,
25% Quartz
10% Mica, Amphibole
Sedimentary Rocks:
Mudstones, Sandstones, Carbonates

9. Crust Composition: Rock Type
Continental Crust:
Granite ~ 60% Feldspar,
25% Quartz
10% Mica, Amphibole
Sedimentary Rocks:
Mudstones, Sandstones, Carbonates

10. Net Result: Grain Types
Most common grains produced is some type of Feldspar (~60% of granitic crust)
But Feldspar weathers rapidly
Quartz, already abundant, is enhanced on Earth surface because it is resistant to weathering
Rock Fragments – mostly sedimentary, but can be metamorphic or volcanic
Note: Granite or Gneiss rock fragments are classified with Feldspar

11. Breakdown of Primary Grain Types
Quartz
Plutonic = “common quartz”
Volcanic
Metamorphic = composite/polycrystalline
Recycled sediment
Vein (from final magmatic stages)
Feldspar
Alkali Feldspar (Mostly K-Feldspar = K-spar)
Plagioclase
Intergrowths of K-spar & Plagioclase
Rock fragments
Sedimentary (SRF)
Metamorphic (MRF)
Volcanic (VRF)

12. End of Part 1

13. Sedimentology Grain Mineralogy (2): Quartz Reading Assignment: Boggs, Chapter 5

14. Quartz Mineral Characteristics
Hardness (7).
Chemically stable SiO2 tetrahedron
Can be present in:
monocrystalline form- (most stable)
composite grains
Quartz is the most common sedimentary grain (65% of average sandstone)
How do we identify it in thin section?
Extinction under polarized light (straight to highly undulatory)
Grain shape (subequant to bipyramidal)
Inclusions & vacuoles
Colors ranges from clear to a wide variety of colors caused by inclusions

15. Quartz extinction in polarized light

16. Extinction in granitic quartz

17. Undulose extinction in stressed quartz

18. Range of Extinction
Straight extinction

19. Range of Extinction
Slightly Undulose Extinction

20. Range of Extinction
Strongly Undulose

21. Inclusions & Vacuoles
Inclusions/vacuoles look like needles or bubbles within the quartz crystal

22. Plutonic Quartz monocrystalline
Typically from granitic source (continental crust)
The ultimate weathering product from granite
Characteristics
monocrystalline
Subequant shape
Straight extinction with polarized light
Few vacuoles or inclusions
Sub-equant
Straight extinction

23. Volcanic Quartz Volcanic source Distinctive bipyramidal shape
Straight extinction
Few inclusions or vacuoles
bipyrimidal
vacuoles

24. Metamorphic Quartz Sutured contacts Undulatory extinction
Composite/polycrystalline
Interlocking crystals, sutured contacts
Can be elongate (schist)
Undulatory to strongly undulatory extinction
Sutured contacts
Undulatory extinction
polycrystalline

25. Metamorphic Quartz polycrystalline polycrystalline
Composite/polycry stalline
Interlocking crystals, sutured contacts
Can be elongate (schist)
Undulatory to strongly undulatory extinction
polycrystalline

26. Vein Quartz
Forms in final magmatic stage (plutonic bodies) where volatiles are abundant
Common vacuoles & inclusions (often called “milky” Quartz)

27. End of Part 2

28. Sedimentology Grain Mineralogy (3): Feldspars Reading Assignment: Boggs, Chapter 5

29. Feldspar Family Alkali feldspar –
Solid solution series from KAlSi3O8 → (K, Na)AlSi3O8 → NaAlSi3O8
Most common are K-feldspar
Orthoclase (KAlSi3O8)
Microcline (NaAlSi3O8)

30. Feldspar Family Alkali feldspar –
Solid solution series from KAlSi3O8 → (K, Na)AlSi3O8 → NaAlSi3O8
Most common are K-feldspar
Orthoclase (KAlSi3O8)
Microcline (KAlSi3O8)
Plagioclase feldspar-
Solid solution series from NaAlSi3O8 (Albite) → CaAl2Si2O8 (Anorthite)
General formula (Na,Ca)(Al, Si)Si2O8

31. Feldspar Mineral Characteristics
Most common mineral in Earth crust
Hardness (6) = less than Quartz
Chemically unstable, commonly altered, weathers to clay minerals
Pink, white, gray, brown in color
Untwinned to distinctive twinning habit in Plagioclase & Microcline
K-spar appears similar to Quartz, identified by staining techniques

32. K-Feldspar – Staining to differentiate from quartz

33. K-Feldspar – Grid Twinning in Microcline

34. K-Feldspar – Grid Twinning in Microcline

35. K-Feldspar – Dissolution & Alteration

36. Plagioclase - Twinning

37. Plagioclase – Alteration & Dissolution

38. Perthite – Intergrowth of K-Spar & Plagioclase

39. End of Part 3

40. Sedimentology Grain Mineralogy (4): Quartz Reading Assignment: Boggs, Chapter 5

41. Rock Fragments Sedimentary rock fragments (SRF)
Chert – microcrystalline quartz
Glauconite – marine, typically from fecal pellets or organic material
Shale, siltstone, mudstone, sandstone
Metamorphic rock fragments (MRF)
Slate, schist (gneiss is considered Feldspar for classification)
Volcanic rock fragments (VRF)
Glass, tuff

42. Rock Fragments- SRF

43. SRF – Claystone & Shale

44. SRF - Siltstone

45. SRF - Sandstone

46. SRF – Limestone, Fossil, Dolomite

47. SRF - Chert

48. Rock Fragments- MRF

49. MRF - Slate

50. MRF - Schist

51. Rock Fragments- VRF
Glass, dissolution
Tuff w/ Glass shards

52. Rock Fragments- Plutonic

53. Other Grains - Biogenic
Glauconite
Plant
Red algae
Coal

54. Other Grains - Inorganic
Heavy minerals (s.g. > 2.9)
Most common zircon (very stable) ,rutile, magnetite (opague), pyroxene, amphibole, mica

55. Other Grains - Inorganic
Muscovite
Opaque Mineral
Zircon
Amphibole

56. Classification – Primary Tool for Determining Source Area/Provenance

57. Questions You Should be Able to Answer
How many naturally occurring elements? Which are most common in the Earth’s crust? What are the 2 most common?
What are silicate minerals? Why are they so common in the Earth’s crust? What are the common silicate minerals? Which two are most common?
What are common groups of non-silicate minerals?
What is the general mineral composition of granite?
What rock types compose the crust by volume? By surface cover?
What is the most common sedimentary rock?
What are the 3 main types of sedimentary grains?
What are the characteristics of the mineral Quartz?
What are the origins of Quartz grains? What are the distinguishing characteristics of each type? Which type is most common? Why?
What does the extinction pattern in Quartz tell you?
What are inclusions in grains? Vacuoles? How do they form?

58. 12. What are the characteristics of Feldspars?
13. What is the overall structure of the family of Feldspar minerals? How do these plot on a tertiary diagram?
14. What are Alkali Feldspars? What are the most common types? What is the general chemical composition? What are the distinguishing characteristics that allow you to identify these?
15. What are Plagioclase Feldspars? What are the most common types? What is the spectrum in chemical composition across this solid-state series? What are the distinguishing characteristics that allow you to identify these?
16. How do you identify mineral alteration to clay and dissolution in Feldspars?
17. What types of intergrowths of Feldspar minerals are common?
18. What are the main types of rock fragments seen as sedimentary grains?
19. What is chert?
20. What is glauconite?
21. What features allow you to identify a sedimentary rock fragment?

59. 22. What are the types of metamorphic rock fragments
22. What are the types of metamorphic rock fragments? How would you identify these?
23. How do you identify igneous rock fragments?
24. What is the basis for classification of grains on the standard tertiary diagram? You need to be able to reproduce this diagram, and know the composition of Quartzarenite, Arkose, Litharenite, etc…
25. What is the purpose of the classification of grains by mineralogy/type?