Unit – 2Mineralogy

A mineral:A mineral: is a naturally occurring inorganic crystalline is a naturally occurring inorganic crystalline

solidsolid has an ordered internal arrangement of atomshas an ordered internal arrangement of atoms has specific physical properties that are either has specific physical properties that are either

fixed or that vary within some defined range.fixed or that vary within some defined range. has a definite chemical composition that may has a definite chemical composition that may

vary within specific limitsvary within specific limits

Types of minerals

Comman rock-forming minerals

(eg: feldspar,quartz,mica,kyanite etc)Economic minerals

(eg:hematite,galena,chrimite,magnesite etc)

Importance of mineralogy

As different rocks are used in different civil constructions so as a civil engineer we must be know to enable them to consider different rocks for different construction purposes. Knowledge of properties like strength, durability, and appearance of rocks can be assessed by only with the knowledge of minerals that forms rocks.

Different methods of study of minerals

Study of physical properties

Study of chemical properties

Study of optical properties

X-ray analysis

Study of Physical Properties of Minerals Form Colour Streak Luster Fracture Cleavage Hardness Specific gravity Degree of transparency Special Properties Other Properties

Importance of Physical properties of minerals

Since every mineral possess different physical properties so it is easy to know about the mineral by knowing its physical properties.

From the civil engineering point of view it is very important to know the physical properties of minerals to use them in different constructions.

1. Form:

Form is nothing but the physical appearance of mineral. It I also called as structure of the mineral.

Tabular form: mineral occurs in the form of a flattened, square, rectangular shape with uniform thicknessLamellar form: mineral appears as thin separable layers.Bladed form: mineral appears as if composed of thin, flat, parts as it is cutted with blade.

Bladed form

Granular form: mineral appears in the form of densely packed grains.

Massive form: no definite shape for minerals.

Reni form: mineral appears with no. of overlapped kidney-shaped structures.

Granular form Massive form Reni form

2. Colour: The colour of the any mineral is a light dependent property. Sometimes it is because of the presence of trace elements, sometimes due to composition.

3. Streak: It is the colour of mineral powder. Different minerals exhibit different streak most of them exhibit white colour.

4. Lusture: It is the shining property of mineral. It is dependent on;•The refractive index•The absorption capacity if light•The nature of reflecting surface

Typical lustures of minerals

Metallic: shines like a metal. Eg: galena Vitreous: shines like a glass. Eg: quartz Pearly: shines like a pearl. Eg: mica Silky: shines like a silk. Eg: gypsum Resinous: shines like a resin. Eg:opal Greasy: shines like a grease. Eg: graphite Dull: shine is almost absent. Eg: chalk. Adamantine: shines like a diamond. Eg:

diamond

5. Fracture: It is the nature of the randomly broken surface of a mineral. It is less useful property of mineral because most of the minerals shows same fracture.

Typical fractures of minerals• Even : broken surface is smooth and flat. Eg: chalk• Uneven: broken surface is irregular. Eg: most of the minerals.• Hackly: broken surface is irregular with separable layers. Eg:

asbestos.• Conchoidal: broken surface shows concentric rings. Eg: opal• Sub-conchoidal; broken surface shows concentric rings with

less curvature. Eg:agate

chalk talc

biotite

opal

6. Cleavage:

The definite direction or plane along which a mineral tends to break is called cleavage.

7. Hardness:

It may be defined as the resistance offered by mineral to scratching.Based upon the Moh’s scale of hardness minerals are arranged according to their hardness from 1 to 10.

8.Specific gravity(density):

Density of a mineral is defined as mass per unit volume of the mineral.

Density types of minerals

Low density - sp.gravity<2.5Medium density - sp.gravity 2.5 to 3.5High density - sp.gravity>3.5

9. Degree of transparency: The property of the mineral to pass light through it.They may be classified as,•Transparent•Translucent•opaque

10. Special properties: some minerals exhibit special properties.

Advantages of study of minerals by physical properties

Study of mineral in field it self. Does not require any equipment No need of chemicals No loss or wastage of minerals Quickest method Cheapest, simplest and least tedious

Study of chemical composition

From definition minerals have its own distinctive chemical composition. If the composition is known it is easy to identify the mineral.

Study of optical properties

Making use of polarized light under crossed nicols, different optical properties of the minerals like colour, refractive index, total refraction etc. are studied.

Polarising microscope

X-ray analysis

It make use of the atomic structure of the mineral to identify them. X-rays are similar to light waves but have a much shorter wavelength.

Atomic structure of mineral by x-ray analysis

From: http://www.geology.fau.edu/course_info/fall02/gly4200/X-RAY.htm