1. Structure of the Silicate Minerals
Comparing Crystal Structures to
Visible Mineral Properties

2. Silicon, Silicates, Silicones How to Tell the Difference
Silicon: One of 92 naturally occurring chemical elements

3. Silicon, Silicates, Silicones How to Tell the Difference
Silicon (cont.):
Silicon is a metalloid: Its nucleus is comprised of:
14 protons
14 neutrons surrounded by:
14 electrons.

4. Silicon

5. Silicon, Silicates, Silicones How to Tell the Difference
Silicon (cont.):
Rarely found as a pure substance
Silicon shines with metallic luster.
Silicon Wafer

6. Silicon structure
Silicon (cont.): Like carbon, silicon is capable of linking together with other atoms to make large molecules.

7. Silicon, Silicates, Silicones How to Tell the Difference
Silicates: Atoms join together to make molecules. Each silicate mineral is made of molecules.
90 % of Earth’s rocks are made of silicate minerals.

8. Silicon, Silicates, Silicones How to Tell the Difference
Silicates (cont.): Quartz Sand
the simplest silicate molecule -
formed by joining one silicon atom with two oxygen atoms.
SiO2
Sand Grains

9. It is used to soak up moisture.
Silica GeL
Silica Gel is man-made.
It is used to soak up moisture.

10. Silicates

11. Metallic Silicon + Oxygen Gas combine to make…
Silicates
Metallic Silicon + Oxygen Gas combine to make…

12. …glassy silicate gemstones.
Silicates
…glassy silicate gemstones.

13. Silicate Tetrahedron
Silicates are classified on the basis of the arrangement of their silicate tetrahedra:
Oxygen
The culprit: the [SiO4]4- tetrahedron
Silicon

14. Silicon, Silicates, Silicones How to Tell the Difference
long, rubbery molecules
quite different from silicates
not like minerals at all.

15. Silicon, Silicates, Silicones How to Tell the Difference
Silicones (cont.):
– Si – O – Si – O – Si – O backbone
carbon-based (organic) molecular groups attached to the
silicon atoms.

16. Silicones
Silicones: Used for:
Silicone caulk
Silicone cement or glue

17. Silicones
Silicones: Used for:
Lubrication and
Waterproof coatings

18. Silicones
Silicones:
Used to simulate flesh in cosmetic surgery (facial reconstruction and breast implants).

19. Silicones
Silicones:
Used to simulate flesh in cosmetic surgery (facial reconstruction and breast implants).

20. Structure of the Silicate Minerals
Comparing Crystal Structures to
Visible Mineral Properties

21. I. Independent Tetrahedra Structure:
Tetrahedra are not directly linked together.
Oxygen “corners” of tetrahedra are linked by metallic ions such as iron (Fe).

22. I. Independent Tetrahedra Structure:
Olivine, a olive-green silicate mineral in basalt
Tetrahedra are linked by iron atoms, which rust out easily
Causes the tetrahedra to fall apart.

23. I. Independent Tetrahedra Structure:
As a result, olivine is often granular and crumbly. Ex: Olivine, Kyanite, Garnets, Topaz

24. Other Independent Tetrahedra Minerals
Kyanite

25. Other Independent Tetrahedra Minerals
Garnet

26. Other Independent Tetrahedra Minerals
Topaz / Staurolite

27. II. Chain Structure: Chains can be single chain or double chain.
In single chain silicates, each tetrahedra shares two of its four oxygen “corners” with two other tetrahedra.

28. II. Chain Structure: Chains can be single chain or double chain.
Test Question: How many oxygen atoms is Silicon atom X sharing with its neighbors?

29. II. Chain Structure:
In a double chain silicate, a third oxygen “corner” is shared between tetrahedra from two parallel chains.

30. II. Chain Structure:
Chains of tetrahedra are held together by linking metallic ions:
Linking bonds are much weaker than the Si–O bonds of the tetrahedra,
causes chain silicates to have a stringy or fibrous texture.

31. Inosilicates: single chain- pyroxenes
= Layers of purple Mg and yellow Ca ions create weak bonds and cleavage planes

32. II. Chain Structure:
Actinolite is a good example of a fibrous chain silicate.

33. II. Chain Structure:
Hornblende and Augite are common Chain Structure minerals.

34. Typical stringy, fibrous chain silicates
Inosilicates: single chain STRUCTURE - pyroxenes –
Pectolite & Wollastonite
Typical stringy, fibrous chain silicates

35. Inosilicates: single chain- pyroxenes – Kunzite
A chain silicate gemstone

36. Inosilicates - Double Chain Structure
Test Question: How many oxygen atoms is Silicon atom X sharing with its neighbors now?

37. Inosilicates - Double Chain Structure – Actinolite & Tremolite
Typical stringy, fibrous chain silicates

38. Cyclosilicates – Ring Structure

39. Cyclosilicates – Ring Structure
Two oxygen “corners” are shared with other silicate tetrahedra.
The tetrahedra joined in rings of , 4, or 6 tetrahedra.
Ring structures are not common.
Ring structure - usually long barrel- shaped crystals (hexagonal prisms).

40. Cyclosilicates –
Ring
Structure -
Emerald

41. Cyclosilicates: Ring Structure Aquamarine

42. Cyclosilicates –
Ring Structure
Red Beryl

43. Cyclosilicates – Ring Structure
Tourmaline

44. IV. Sheet Structure:
Every tetrahedra shares all three of its base “corners” with three neighboring tetrahedra to form continuous flat sheets of
tetrahedra.

45. IV. Sheet Structure:
Six tetrahedra form a basic hexagonal shape which is repeated over and over.

46. IV. Sheet Structure:
How many of its 4 oxygen atoms is Silicon atom Z sharing with its neighbor Silicons?

47. IV. Sheet Structure:
Fourth oxygen “corner” of each tetrahedra is pointing either up or down.
(See Side
View on
next slide.)

48. IV. Sheet Structure:
Fourth corners are linked to layers of metals (K, Al, Fe, Mg)
Metals are linked to the “corners” sticking out of the next sheet of tetrahedra.
Looks like a
silicate / metal
“sandwich”.
SiO2 Sheet
SiO2 Sheet
Metal Layer
SiO2 Sheet
SiO2 Sheet

49. IV. Sheet Structure: Metallic linking bonds:
are much weaker than the Si – O bonds within each sheet, so they
break easily.

50. IV. Sheet Structure: Muscovite and Biotite Mica: Are sheet silicates
Split easily into paper-thin sheets
Have perfect one direction cleavage.

51. Phyllosilicates - Sheet Structure Muscovite Mica

52. Phyllosilicates - Sheet Structure Biotite Mica

53. Phyllosilicates - Sheet Structure LEPIDOLITE Mica

54. Phyllosilicates - Sheet Structure Chrysacolla
Chrysacolla is a sheet silicate, but it is made of microscopic flat flakes.

55. Phyllosilicates - Sheet Structure Chrysacolla
Kaolinite (clay) is a sheet silicate, but it is made of microscopic flat flakes.

56. Phyllosilicates - Sheet Structure Talc
Talc is made of small, flat flakes that slide over each other easily – causes talc’s “soapy” feel.

57. Phyllosilicates - Sheet Structure Talc

58. 3-Dimensional Framework
Si Tetrahedra shares all four “corners” with its four neighboring tetrahedra … W

59. 3-Dimensional Framework
…to form a continuous 3-dimensional network or framework.

60. 3-Dimensional Framework

61. 3-Dimensional Framework
Bonds are equally strong in all directions.
Produce minerals that are exceptionally hard.

62. 3-Dimensional Framework
Bonds are equally strong in all directions:
Minerals do not break with cleavage
no layers of weak bonds to give way.
Rose Quartz
Milky Quartz

63. 3-Dimensional Framework Structure - Quartz

64. 3-Dimensional Framework Structure - Quartz
Rock Crystal Quartz

65. 3-Dimensional Framework Structure - Quartz
Citrine
Rose Quartz

66. 3-Dimensional Framework Structure - Quartz
Chert
Jasper

67. modified Framework
Some of the silicon ions are replaced by metal ions (K, Al, Na, and Ca).
Na Feldspar
K Feldspar

68. SiO2 modified Framework
Start with a regular framework mineral (Milky Quartz):
SiO2
Milky Quartz

69. Si2O4 modified Framework
Keep the Si:O ratio at 1:2 and it’s still quartz.
Si2O4
Milky Quartz

70. Si4O8 modified Framework
Keep the Si:O ratio at 1:2 and it’s still quartz.
Si4O8
Milky Quartz

71. modified Framework
Remove one of the Silicons (Si4+)…
Si4O8
K Feldspar

72. modified Framework
Remove one of the Silicons (Si4+)…
Si3O8
K Feldspar

73. AlSi3O8 modified Framework …and replace it with an Aluminum ion (Al3+)
K Feldspar

74. KAlSi3O8 modified Framework
Still need another +1 metal ion to balance out the charges ( K+ or Na+ )
KAlSi3O8
K Feldspar
Et voilà– le’ Framework Modifiée!! (Modified Framework Structure)

75. 3-Dimensional Framework
Layers of metal ions create layers of weak bonds
Modified Framework minerals do have cleavage planes.
K Feldspar
Na Feldspar

76. 3-Dimensional Framework Structure - Feldspars
Amazonite Feldspar

77. 3-Dimensional Framework Structure - Feldspars
Albite Feldspar
Labradorite Feldspar

78. 3-Dimensional Framework Structure – Sodalite

79. SUMMARY
Many visible physical properties of minerals are reflections of their atomic structure:

80. The scaly micas split along parallel cleavage planes due to their
SUMMARY
The scaly micas split along parallel cleavage planes due to their
sheet structure:

81. SUMMARY
Some amphiboles such as actinolite are fibrous (stringy) due to their chain structure.

82. SUMMARY
Olivine weathers easily because the iron atoms that link its independent tetrahedra rust out, causing the tetrahedra to fall apart.

83. Quartz is hard and shows no cleavage because its tetrahedra form a
SUMMARY
Quartz is hard and shows no cleavage because its tetrahedra form a
3 – Dimensional Framework which is equally strong in all directions.

84. SUMMARY
The explanation for all of a mineral’s properties can be found among its atoms.