Phyllosilicates Structure and Properties

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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?

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

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

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

What is the characteristic feature of chlorite minerals?

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

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

Their layered structure (B) Signup and view all the answers

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

2:5 (A) Signup and view all the answers

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

Brucite sheet (A) Signup and view all the answers

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

3+ (D) Signup and view all the answers

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

Their relative chemical inertness (A) Signup and view all the answers

What is the difference between dioctahedral and trioctahedral phyllosilicates?

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

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

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

What is the name given to fine-grained muscovite?

Sericite (B) Signup and view all the answers

What is the significance of polytypism in phyllosilicates?

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

What is the significance of the pseudohexagonal habit of biotite?

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

What is the main difference between muscovite and illite?

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

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

As insulators (D) Signup and view all the answers

What is the characteristic of the octahedral sheet in phyllosilicates?

It is composed of MeO6 octahedra (C) Signup and view all the answers

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

Trioctahedral phyllosilicate (B) Signup and view all the answers

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

Mg(OH)2 (A) Signup and view all the answers

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

Quartz (C) 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?

Dioctahedral and trioctahedral (C) Signup and view all the answers

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

Al(OH)3 (D) Signup and view all the answers

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

Serpentine group (D) Signup and view all the answers

What is the characteristic feature of the structure of antigorite?

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

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

Crocidolite (A) Signup and view all the answers

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

Mg3Si2O5(OH)4 (B) 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?

Serpentine (C) Signup and view all the answers

What is the characteristic feature of the structure of chrysotile?

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

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

Stacking pattern of the layers (D) Signup and view all the answers

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

Brittle mica (D) 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?

Margrite (D) Signup and view all the answers

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

T-O-T layer structure (C) Signup and view all the answers

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

KAl2(AlSi3)O10(OH)2 (A) Signup and view all the answers

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

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