Phyllosilicates Structure and Properties
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Questions and Answers

What is a characteristic feature of polytypes?

  • Change in symmetry and environment of ions within sheets
  • Change in the hardness of the mineral
  • Change in the chemical composition of the mineral
  • Change in crystallographic system and/or Bravais type of unit cell (correct)

Why are most micas monoclinic rather than hexagonal?

  • Because they have a monoclinic crystal structure
  • Because their c axis is parallel to the sheets
  • Because they have a hexagonal crystal structure
  • Because their c axis is inclined relative to the sheets (correct)

What is the likely composition of the garnet replaced by chlorite in a pseudomorph?

  • Ca3Al2(SiO4)3
  • CaAl2(Si2O7)(SiO4)(O,OH)2
  • Fe3Al2(SiO4)3 (correct)
  • Mn3Al2(SiO4)3

What is the difference between 'brittle' micas and true micas?

<p>'Brittle' micas are harder and less flexible than true micas (C)</p> Signup and view all the answers

What is the result of substituting Al3+ for Si4+ in tetrahedra?

<p>A charge imbalance that requires coupling for charge balance (A)</p> Signup and view all the answers

What is the characteristic feature of chlorite minerals?

<p>They are low-grade metamorphic minerals (B)</p> Signup and view all the answers

What is the characteristic that allows phyllosilicates to exchange ions with fluids in their surroundings?

<p>Their layered structure (B)</p> Signup and view all the answers

What is the T:O ratio in the tetrahedral sheet of phyllosilicates?

<p>2:5 (A)</p> Signup and view all the answers

What type of sheet is identical to the basic structural unit of the mineral Mg(OH)2?

<p>Brucite sheet (A)</p> Signup and view all the answers

What is the valence of the metallic cations filling the octahedral sheet in dioctahedral phyllosilicates?

<p>3+ (D)</p> Signup and view all the answers

What is the characteristic that makes phyllosilicates versatile in everyday products?

<p>Their relative chemical inertness (A)</p> Signup and view all the answers

What is the difference between dioctahedral and trioctahedral phyllosilicates?

<p>The valence of the metallic cations filling the octahedral sheet (B)</p> Signup and view all the answers

What is the main difference between the structure of dioctahedral muscovite and trioctahedral lepidolite?

<p>The number of ions in the octahedral sheet (B)</p> Signup and view all the answers

What is the name given to fine-grained muscovite?

<p>Sericite (B)</p> Signup and view all the answers

What is the significance of polytypism in phyllosilicates?

<p>It refers to the different stacking geometries of phyllosilicate layers (D)</p> Signup and view all the answers

What is the significance of the pseudohexagonal habit of biotite?

<p>It shows the size misfit between tetra- and octahedral sheets (C)</p> Signup and view all the answers

What is the main difference between muscovite and illite?

<p>The substitution of magnesium and calcium for potassium (C)</p> Signup and view all the answers

What is the use of muscovite and Fe-free phlogopite in electrical devices?

<p>As insulators (D)</p> Signup and view all the answers

What is the characteristic of the octahedral sheet in phyllosilicates?

<p>It is composed of MeO6 octahedra (C)</p> Signup and view all the answers

Which type of phyllosilicate has a valence of 2+ for the metallic cations in the octahedral sheet?

<p>Trioctahedral phyllosilicate (B)</p> Signup and view all the answers

What is the name of the mineral that has a similar structure to the 'brucite' sheet?

<p>Mg(OH)2 (A)</p> Signup and view all the answers

Which of the following minerals is not a type of phyllosilicate?

<p>Quartz (C)</p> Signup and view all the answers

What is the term for the subdivision of phyllosilicates based on the valence of the metallic cations in the octahedral sheet?

<p>Dioctahedral and trioctahedral (C)</p> Signup and view all the answers

What is the name of the mineral that has a similar structure to the 'gibbsite' sheet?

<p>Al(OH)3 (D)</p> Signup and view all the answers

What is the name of the mineral group that includes antigorite, lizardite, and chrysotile?

<p>Serpentine group (D)</p> Signup and view all the answers

What is the characteristic feature of the structure of antigorite?

<p>The layers are curved but reverse orientation regularly (A)</p> Signup and view all the answers

What is the name of the mineral that is often referred to as 'blue asbestos'?

<p>Crocidolite (A)</p> Signup and view all the answers

What is the composition of the minerals in the serpentine group?

<p>Mg3Si2O5(OH)4 (B)</p> Signup and view all the answers

What is the term for rocks that are made up mostly of minerals from the serpentine or clay group?

<p>Serpentine (C)</p> Signup and view all the answers

What is the characteristic feature of the structure of chrysotile?

<p>The layers are curved and rolled up like a carpet (B)</p> Signup and view all the answers

What is the structural characteristic of lepidolite that differs among its three polytypes?

<p>Stacking pattern of the layers (D)</p> Signup and view all the answers

What is the mineral that forms as an alteration mineral in silica-poor rocks, often with corundum?

<p>Brittle mica (D)</p> Signup and view all the answers

What is the result of substituting Al3+ for Si4+ in tetrahedra, with charge balance maintained by coupling with another cation?

<p>Margrite (D)</p> Signup and view all the answers

What is the characteristic of the chlorite group that distinguishes it from other minerals?

<p>T-O-T layer structure (C)</p> Signup and view all the answers

Which mineral is a flexible muscovite with a specific chemical composition?

<p>KAl2(AlSi3)O10(OH)2 (A)</p> Signup and view all the answers

What is the significance of polytypes in minerals with definite sheet structures?

<p>They have different stacking patterns of layers (C)</p> Signup and view all the answers

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