Chapter 9

Question 1

Chain Silicate Structure

Answer 1

Forms when 2 of a tetrahedron’s oxygen atoms are shared with adjacent tetrahedra to form a chain structure.

Each chain has a net excess if negative charges.

Silicon to Oxygen Ratio is 1:3 (pyroxene)

Question 2

Isolated silicate structure

Answer 2

Silicate minerals that are structured so that none of the oxygen atoms are shared by tetrahedra.

Individual silicon-oxygen tetrahedra are bonded together by positive charged ions.

(Olivine) contains 2 ions of either Mg2+ or Fe2+ for each silicon-oxygen tetrahedron.

Question 3

Sheet Silicates

Answer 3

Structure in which each tetrahedron shares 3 oxygen atoms to form a sheet.

(Mica and clay) positive ions hold sheet together are sandwiched between silicate sheets.

Question 4

Framework Silicates

Answer 4

Structure when all four oxygen atoms are shared by adjacent tetrahedra.

(Quartz and Feldspars).

Question 5

Cleavage

Answer 5

Is the ability of a break, when struck or split, along preferred planar directions.

A mineral tends to break along certain planes because the bonding is weaker in those regions.

Quality of cleavage can vary also, adds to diagnostic value. Perfect cleavage means cleaner break.

Quartz has no cleavage because all bonds are equally strong in all directions.

Most useful diagnostic tool because it remains identical from a given mineral sample to another.

Question 6

Silicon-Oxygen Tetrahedron

Answer 6

SiO4(4-)

Basic building block of a crystal.

Atoms are strongly bonded together and the negative charges exceed the positive charges.

Question 7

Polymorphs

Answer 7

Different crystal structures that have the same composition.

Ex: graphite and diamond.

Question 8

Ferromagnesian Minerals

Answer 8

Composed of iron/magnesium bearings.

Often black and dark green in color.

Ex: Augite, olivine, biotite…

Question 9

Physical Properties of Minerals

Answer 9

Color
Streak
Luster
Hardness
External Crystal Form
Cleavage
Fracture
Specific Gravity
Striations

Question 10

Luster

Answer 10

The quality and intensity of light that is reflected from the surface of a mineral.

Either Metallic or Non-metallic
(aka. vitreous/ glassy) or earthy lusters possible.

Luster is described by comparing to familiar substances.

Question 11

Hardness

Answer 11

The “scratchability” of a mineral.

Can be tested fairly reliably, by seeing if the harder substance can create a groove or scratch on a softer substance.

Ex: Quartz can always scratch calcite or feldspar, so it is harder on the hardness scale.

Question 12

Mohs’ Hardness Scale

Answer 12

Measures of force necessary to make an indentation on a substance.

10 minerals are designated as standards of hardness::

Talc: softest on scale
Gypsum:
Calcite: fingernail hardness
Fluorite: copper coin hardness
Apatite: knife blade/ window glass
Feldspar: 
Quartz: Almost steel file hardness
Topaz:
Corundum:
Diamond: hardest on scale

Question 13

External Crystal Form

Answer 13

Is the set of faces that have definite geometric relationship to one another.

Crystals commonly consist of several types of forms combined to generate the full body of each sample.

Regularity in nature can be good diagnostic property, as minerals that display crystal form have sets of angles for adjacent faces that never vary from sample to sample for a given mineral.

Question 14

Fracture

Answer 14

The way a substance breaks where not controlled by cleavage.

Minerals that have no cleavage(quartz and garnet) often have an irregular fracture.

Minerals with cleavage can also “fracture” along directions other that of the cleavage.

Conchoidal Fractures: breaks along curved fracture surfaces (looks like clam shell).

Question 15

Specific Gravity

Answer 15

Common expression of Density.

Ratio of a mass of a substance to the mass of an equal volume of water.

Liquid water: 1
Ice: 0.9
Quartz: 2.65
Feldspars: 2.56 - 2.76
Gold: 19.3

Question 16

Striations

Answer 16

Straight, parallel lines on the flat surfaces of one of the two cleavage directions.

Ex: plagioclase, tourmaline.

Question 17

Acid Fizz Test

Answer 17

One chemical reaction that is routinely used for identifying minerals…

Adding a drop of weak acid(those containing CO3 anion) to a mineral sampling and looking for fizzing(CO2 gas).

Question 18

How do various feldspars differ from one another chemically?

Answer 18

Depends mainly on size/atomic radii of elements. Lined up based on what ions can sub into for others.

Alkali feldspars vs Plagioclase feldspars differ chemically by having K+, Na+, or Ca+ replace each other at the same location in the crystalline structure.

Question 19

What is the distinction between cleavage and external crystal form?

Answer 19

Both produce flat sides and sharp edges, but cleavage is how the mineral breaks, whereas crystal form is how the mineral grows.

Cleavage faces are usually much shinier and flatter than crystal growth faces.

Question 20

Distinguish following on basis of physical properties:

Quartz/feldspar
Calcite/feldspar
Muscovite/feldspar
Pyroxene/feldspar

Answer 20

Feldspars: cleavages at 90 degree angles, doesn’t fizz during acid test, white or pinkish in color.

Quartz: usually has conchoidal fractures

Muscovite: 1 cleavage, thin flexible sheets.

Pyroxene: dark green in color

Calcite: fizzes with acid test.

Question 21

What major factor controls chemical activity between atoms?

Answer 21

Temperature. Also, valence electrons.

Question 22

What are the three most common elements in the Earth’s crust?

Answer 22

Oxygen 47%
Silicon 28%
Aluminum 8%