Mineralogy

Question 1

What is a mineral?

Answer 1

Any naturally occurring inorganic substance with a definite chemical composition and characteristic crystalline structure, color, and hardness.

Question 2

How many minerals are there?

Answer 2

There are approximately 4000 varieties of minerals which can be classified into one of eight major mineral classes similar to how biologists classify living organisms into groups such as plants, animals, fungi, and bacteria.

Question 3

How are minerals classified?

Answer 3

Minerals, however, are classified into groups by their composition and crystal structure. Ninety five percent of the rocks found in Earth’s crust contain minerals known as silicates.

Question 4

What is hardness?

Answer 4

Hardness is the ability of a material to resist abrasion when a pointed fragment of another substance is drawn across it without sufficient pressure to develop fracture or cleavage.

Question 5

Why determines the hardness of a mineral?

Answer 5

Differential structure is related to both the crystal and atomic structure of the diamond crystal.

Question 6

What is differential hardness?

Answer 6

Diamonds have differential hardness which means the hardness differs with the direction of scratching in certain gem materials. This differential hardness is due to the arrangement of the atomic bonding in crystal structures.

Question 7

What is an impurity

Answer 7

Foreign material, such as elemental additions, within a mineral’s structure that are not part of its integral structure. Impurities are often responsible for color changes.

Question 8

What factors influence color in minerals?

Answer 8

1. Elements
2. Chemical impurities
3. Defects in crystal structures
4. Mechanical mixture of fine impurities
5. Finely spaced structures in the mineral

Question 9

What is color?

Answer 9

Result of dominant wavelength of light. Minerals are colored because certain wavelengths of incident light are absorbed, and the color we perceive is produced by the remaining wavelengths that were not absorbed.

Question 10

Why minerals are colorless?

Answer 10

This means that none of the incident light has been absorbed.

Question 11

Cause of Color Center

Answer 11

Color can also be caused by structural defects in minerals. For example, an excess electron that is unattached to any single atom may be trapped in a structural defect such as a void due to a missing ion. A hole, or the absence of an electron, can have the same effect.

Question 12

Fracture

Answer 12

When a mineral sample is split in a direction which does not serve as a plane of perfect or distinct cleavage. A mineral fractures when it is broken or crushed.

Question 13

Mohs scale

Answer 13

Mohs’ method relies upon a scratch test to relate the hardness of a mineral specimen to the hardness of one of a set of reference minerals.

Question 14

Tenacity

Answer 14

The characteristic of tenacity describes the physical behavior of a mineral under stress or deformation.

Question 15

Brittle

Answer 15

Most minerals are brittle; metals, in contrast, are malleable, ductile, and sectile. Most mineral species are brittle, and will crumble or fracture under pressure or upon the application of a blow. Such materials break or powder easily.

Question 16

Streak

Answer 16

Is the color of a mineral substance when it has been ground to a fine powder.

Question 17

Cleavage Plane

Answer 17

Plane of structural weakness along which a mineral is likely to split smoothly.

Question 18

Cleavage

Answer 18

Cleavage thus refers to the splitting of a crystal between two parallel atomic planes. Cleavage is the result of weaker bond strengths or greater lattice spacing across the plane in question than in other directions within the crystal. Greater lattice spacing tends to accompany weaker bond strength across a plane, because such bonds are unable to maintain a close interatomic spacing.

Question 19

Quality of Cleavage

Answer 19

Refers to both the ease with which the mineral cleaves and to the character of the exposed cleavage surface. Described by terms such as ‘eminent,’ ‘perfect,’ ‘distinct,’ ‘difficult,’ ‘imperfect,’ or ‘indistinct.’

Question 20

Conchoidal fracture

Answer 20

Results in a series of smoothly curved concentric rings about the stressed point, generating a shell-like appearance. The familiar ripples of a broken glass bottle demonstrate this type of fracture.

Question 21

Moh’s Hardness

Answer 21

Talc
    Gypsum
    Calcite
    Fluorite
    Apatite
    Orthoclase
    Quartz
    Topaz
    Corundum
    Diamond

Question 22

Density

Answer 22

As mass per unit volume:

Question 23

Specific gravity

Answer 23

A unit-less quantity which is defined as the ratio of the weight of a substance to the weight of an equal volume of water at a temperature of 4° Celsius. This ratio is equal to the ratio of the density of the substance to the density of water at 4° Celsius.

Question 24

Luster

Answer 24

Refers to the quantity and quality of the light which is reflected from a mineral’s exterior surfaces. Luster provides an assessment of how much the mineral surface ‘sparkles’.

Question 25

Categories of Luster:

Answer 25

Primarily divided into the three categories of metallic, sub-metallic and nonmetallic luster.

Question 26

Metallic Luster

Answer 26

Minerals possessing metallic luster are opaque and very reflective, possessing a high absorptive index.

Question 27

Color Center

Answer 27

The unpaired electron which produces color by light absorption into excited states does not have to be located on a transition element ion; under certain circumstances it can be located on a nontransition-element impurity ion or on a crystal defect such as a missing ion.

Question 28

Electron Color Center

Answer 28

If an electron is present at a vacancy, we have an “electron” color center; if an electron is missing from a location where there usually is an electron pair, we have a “hole” color center.

Question 29

What is an indicator mineral?

Answer 29

Minerals that may indicate possible diamond occurrences.