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Questions and Answers
Different sheet combinations make up these types of ______ of layers:
Different sheet combinations make up these types of ______ of layers:
phyllosilicates
Main groups within the ______ are: 1) serpentine group 2) clay minerals 3) true micas 4) brittle micas 5) chlorite group
Main groups within the ______ are: 1) serpentine group 2) clay minerals 3) true micas 4) brittle micas 5) chlorite group
phyllosilicates
In antigorite, the T-O layers are curved but they reverse orientation ______.
In antigorite, the T-O layers are curved but they reverse orientation ______.
regularly
The result is a “corrugation” (waviness) which prevents the layers from ______ easily over each other.
The result is a “corrugation” (waviness) which prevents the layers from ______ easily over each other.
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In chrysotile, the T-O layers curve and roll up like a ______.
In chrysotile, the T-O layers curve and roll up like a ______.
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The bad name of “asbestos” comes from ______!
The bad name of “asbestos” comes from ______!
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Over long periods of exposure, crocidolite's needle-like crystals are less soluble and more damaging to ______ tissues than chrysotile.
Over long periods of exposure, crocidolite's needle-like crystals are less soluble and more damaging to ______ tissues than chrysotile.
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Serpentine and clay are not only the name of groups of ______.
Serpentine and clay are not only the name of groups of ______.
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Mg3Si2O5(OH)4 is the composition of ______ group minerals.
Mg3Si2O5(OH)4 is the composition of ______ group minerals.
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The neutral T-O layers are held by weak Van der Waals forces and H..O ______ bonds.
The neutral T-O layers are held by weak Van der Waals forces and H..O ______ bonds.
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What is the main reason for the change in crystallographic system and/or Bravais type of unit cell from one polytype to another?
What is the main reason for the change in crystallographic system and/or Bravais type of unit cell from one polytype to another?
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What is the result of the substitution Al3+ for Si4+ in tetrahedra in muscovite?
What is the result of the substitution Al3+ for Si4+ in tetrahedra in muscovite?
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What type of mineral is chlorite?
What type of mineral is chlorite?
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What is the main difference between true micas and brittle micas?
What is the main difference between true micas and brittle micas?
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What type of bond holds the neutral T-O layers together in phyllosilicates?
What type of bond holds the neutral T-O layers together in phyllosilicates?
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What is the characteristic of the 'corrugation' in antigorite?
What is the characteristic of the 'corrugation' in antigorite?
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What is the result of the substitution of Al3+ for Si4+ in tetrahedra in muscovite, in terms of charge balance?
What is the result of the substitution of Al3+ for Si4+ in tetrahedra in muscovite, in terms of charge balance?
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What is the characteristic of the dioctahedral phyllosilicates?
What is the characteristic of the dioctahedral phyllosilicates?
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What is the characteristic of the trioctahedral phyllosilicates?
What is the characteristic of the trioctahedral phyllosilicates?
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What is the most likely composition of the garnet that was replaced by chlorite in a pseudomorph?
What is the most likely composition of the garnet that was replaced by chlorite in a pseudomorph?
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The substitution of Al3+ for Si4+ in tetrahedra in muscovite requires a charge imbalance.
The substitution of Al3+ for Si4+ in tetrahedra in muscovite requires a charge imbalance.
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Octahedral sheets are characteristic of dioctahedral phyllosilicates.
Octahedral sheets are characteristic of dioctahedral phyllosilicates.
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Mesodesmic bonds are responsible for holding the neutral T-O layers together in phyllosilicates.
Mesodesmic bonds are responsible for holding the neutral T-O layers together in phyllosilicates.
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Trioctahedral phyllosilicates have a characteristic T-O-T layer structure.
Trioctahedral phyllosilicates have a characteristic T-O-T layer structure.
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Dioctahedral phyllosilicates have a characteristic corrugation in their layers.
Dioctahedral phyllosilicates have a characteristic corrugation in their layers.
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The substitution of Al3+ for Si4+ in tetrahedra in muscovite results in a change in the crystallographic system of the mineral.
The substitution of Al3+ for Si4+ in tetrahedra in muscovite results in a change in the crystallographic system of the mineral.
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Polytypes are characterized by a change in the chemical composition of the mineral.
Polytypes are characterized by a change in the chemical composition of the mineral.
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Chlorite is a high-grade metamorphic mineral.
Chlorite is a high-grade metamorphic mineral.
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Brittle micas are found in silica-rich rocks.
Brittle micas are found in silica-rich rocks.
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The result of the substitution of Al3+ for Si4+ in tetrahedra in muscovite is a change in the octahedral sheet structure.
The result of the substitution of Al3+ for Si4+ in tetrahedra in muscovite is a change in the octahedral sheet structure.
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Study Notes
Phyllosilicates
- Phyllosilicates are layered structures, consisting of two types of sheets: tetrahedral and octahedral sheets.
- Tetrahedral sheet: SiO4 units share their three basal oxygen to form infinite sheets, with a T:O ratio of 2:5 or 4:10.
- Octahedral sheet: MeO6 octahedra share edges to form infinite sheets, and may be referred to as "brucite" or "gibbsite" sheets depending on composition.
Subdivision of Phyllosilicates
- Dioctahedral phyllosilicates: valence of metallic cations filling the octahedral sheet is 3+ (Al3+).
- Trioctahedral phyllosilicates: valence of metallic cations filling the octahedral sheet is 2+ (Mg2+ or Fe2+).
Weathering and Formation
- Illite forms by weathering of K-feldspar through a hydrolysis reaction.
- Kaolinite forms by weathering of feldspars at the Earth's surface, with crystals remaining small.
- Talc forms at a low grade of metamorphism, with crystals growing larger.
Phyllosilicate Groups
- Serpentine group: three minerals of composition Mg3Si2O5(OH)4, with different sheet structures.
- Clay minerals: can absorb water molecules between the sheets, causing expansion.
- True micas: include phlogopite, biotite, and muscovite.
- Brittle micas: harder and less flexible than true micas, found in silica-poor rocks.
- Chlorite group: low-grade metamorphic mineral, with an extra octahedral sheet.
Smectite Clays
- Smectite clays: have a high cation exchange capacity due to an increased net negative charge.
- Can absorb water molecules between the sheets, causing swelling.
- Used in drilling mud, dam plugs, and to mop up heavy metals.
Illite
- Illite is a general term for mica-like clay minerals with a T-O-T layer.
- Forms from smectite through a temperature-driven reaction, with incorporation of K+ ions between layers.
- No longer swells when moistened due to stronger K-O bonds.
Polytypes
- Polytypes: structural variants found in minerals with definite sheet structures.
- Different stacking patterns of layers result in different crystallographic systems and/or Bravais types of unit cells.
- Most micas are monoclinic rather than hexagonal due to the inclined c axis relative to the sheets.
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Description
This quiz covers the properties and structure of phyllosilicates, a type of mineral commonly used in everyday products. It explores their characteristics, such as cleavage and chemical inertness, and their layered structure.
