Observation: Observation of the mineral to identify the mineral type and its different type of properties.

Pre-requisite

• Basic knowledge of Minerals
• Specimens Availability
• Unglazed porcelain plate (known as a streak plate), hardness scale etc.

You can find the mineral and its properties file in references which is developed by Dr. Sandeep A. Meshram, Associate Professor in Geology, COEP Technological University, Pune.

A mineral is a naturally occurring inorganic solid, with a definite chemical composition, and an ordered atomic arrangement. This may seem a bit of a mouthful, but if you break it down it becomes simpler. Minerals are naturally occurring. They are not made by humans. Minerals are inorganic.

Minerals are classified based on their crystal form and chemistry. Minerals are divided into two types namely metallic and non-metallic. More than 4,000 naturally occurring minerals-inorganic solids that have a characteristic chemical composition and specific crystal structure-have been found on Earth The five most common mineral groups in rock are the silicates, carbonates, sulfates, halides, and oxides. There are about 4000 known minerals in the Earth's crust, and about 92 % of them are silicates. The most abundant silicate is called plagioclase.

The broadest divisions of the classification used in the present discussion are

• native elements
• sulfides
• sulfosalts
• oxides and hydroxides
• halides
• carbonates
• nitrates
• borates
• sulfates
• phosphates
• silicates

Minerals are divided into groups based on chemical composition. Most minerals fit into one of eight mineral groups.

The major classes of minerals are:

• silicates.
• sulfides.
• carbonates.
• oxides.
• halides.
• sulfates.
• phosphates.
• native elements.

Types of minerals:

• Native elements. eg. Gold, Silver, Mercury, graphite, diamond.
• Oxides. eg corundum (incl.sapphire), hematite, spinel.
• Hydroxides. eg. Goethite, brucite.
• Sulfides. eg. Pyrite, galena, sphalerite.
• Sulfates. eg. Baryte, gypsum.
• Carbonates. eg. Calcite, magnesite, dolomite.
• Phosphates.
• Halides.

Minerals can be identified by their color, luster, streak, cleavage, hardness, and even by their chemical composition. Using these properties is one way a Geologist defines and identifies what kind of mineral a specimen is. Most minerals can be characterized and classified by their unique physical properties: hardness, luster, color, streak, specific gravity, cleavage, fracture, and tenacity.

Study of Physical properties and identification of minerals.

Rock forming Minerals: Quartz, Feldspar, Muscovite, Biotite, Augite, Hornblende, Olivine, Garnet, Kyanite, Talc, Chlorite, Flit, Jasper, Asbestos, Calcite etc. Economic Minerals: Bauxite, Magnetite, Hematite, Pyrite and Chromite. Galena, Graphite, Pyrolusite, Magnesite

Identification based on the various physical properties of minerals are as follows

1. Form
2. Colour
3. Streak
4. Luster
5. Fracture
6. Cleavage
7. Hardness
8. Specific Gravity (Density)
9. Degree of Transparency
10. Special Properties.

FORM: This is one of the first observation made when a mineral is examined in a hand specimen. The form represent the common mode of occurrence of a mineral in nature it is also called habit or structure of the mineral. The following is the list of some common forms and the minerals which characteristically exhibit them, i.e., appearance of the particular form is indicative of a certain mineral.

Sr No	Name of the Form	Description	Mineral Example
1	Lamellar Form	Mineral appear separate layers as thin	Different Mica varieties of
2	Tabular Form	Mineral appear as slabs of uniform thickness	Feldspar
3	Fibrous Form	Mineral appear to be made up of fine threads fibers may or may not be separable	Parallel Fibers Asbestos type Satinspar. Radiating Fibers
4	Pisolitic Form	Mineral appear to be made up of small spherical grains(pea-size)
5	Oolitic Form	Similar to Pisolitie but grains are of still smaller size (like fish egg)	Some Limestone's
6	Rhombic Form	Rhombic Shape	Calcite, Dolomite
7	Bladed Form	Mineral appear as cluster or as independent lath shaped (i.e. rectangular grains)	Kyanite
8	Granular Form	Mineral appear to be made up of innumerable equidimensional grains of coarse or medium or fine size	Chromite,Magnetite,Pyrite
9	Reni From	Kidney shaped mineral appear with number of over lapping smooth and somewhat large curved surfaces	Hematite
10	Botryoidal Form	Similar to Reni form but with smaller curved faces like bunch of grapes	Chalcedony Psilomclane hematite
11	Mammillary	Mineral appear with large mutually interfering spheroidal surface - similar to Reni form	Malachite
12	Acicular Form	Mineral appear to be made up of thin needles	Natrolitc, Actinolite
13	Columnar Form	Mineral appear slender prism as long	Tourmaline Topaz
14	Prismatic Form	As elongated indepent crystals	Staucdite, Apatite, Quartz Beryl,
15	Spongy Form	Porous	Pyrolusite, Bauxite
16	Crystal Form	Polyhedral, Geometrical Shapes	Garnet, some Zeolites, Quartz, Amethyst, Pyrite, Galena
17	Interpenetrating Twin Form		Starurolitc
18	Massive Form	No definite shape for mineral	Fluorite, Pyrite Calcite, Graphite,Olivine Quartz, Jasper
19	Concretionary Form	Porous and appear due to accretion of small irregularly shaped masses	Laterite
20	Nodular Form	Irregularly shaped impact bodies with curved surface	Flit, Limestone

COLOUR: It depends upon the absorption of some and the reflection of others of coloured ray of white light. Colour of an object depends upon the colour of the reflected rays when all other colour rays are observed the colour of a mineral is often its most striking property.

1. Absorbed light represents energy that has been used to move electrons from energy level to the other.
2. Factors affecting colour of a mineral type of element valence, state, type of bonding type of neighboring atoms, feature of local symmetry.

For Example:

Chemical composition of olivine of 2-end members

1. Fosterite: Mg2 SiO4 White Colour
2. Fayalite: Fl2 SiO4 Dark Bottle Green This is caused by eh Fe2 ion observing the more of the reddish and the violet parts of the spectrum. Therefore, olivine is more or less green according to its iron content. Sometimes impurities cause colour.

Diagnostic colours of some minerals:

1. Galena - Dark Leady Grey
2. Hematite - Dark Leady Grey
3. Graphite - Shining Black
4. Pyrite - Black
5. Olivine - Yellow
6. Muscovite in book form - Silver White Colour
7. Muscovite in thin layers - Colorless
8. Magnesite - Spotless White
9. Opal – Milky white
10. Chromite, Magnetite - Black Commonly Exhibited Colour of some Minerals

Minerals->Colour	Minerals->Colour
Hornblende -> Dark Green	Calcite -> White
Augite -> Greenish Black	Quartz -> White / Colorless
Orthoclase -> White or Shades of Red	Asbestos -> White, Green, Grey, Yellow
Plagioclase -> Grey or White	Jasper -> Red
Microcline -> White, Pink or Green	Flint -> Yellowish Brown
Kyanite -> Blue	Limonite -> Yellow or Brownish
Garnet-> Red	Baryets -> White / Pale Grey
Talc -> White / Pale	Yellow -> Gypsum -> Colorless or White

Minerals which show different colours:

1. Quartz -> Colourless, White, Green, Violet, Grey, Yellow, Pink etc.,
2. Feldspar -> White, Grey, Shades of Red, Green, Dirty, White etc.,
3. Calcite -> Colourless, White, Shades of Red Grey, Yellow etc.,

STREAK: The colour of mineral powder is called streak of a mineral, and may be quite different from that of the mineral mass. An unglazed white porcelain plate called a streak plate is used in the lab for testing the streak of a mineral. It is conveniently obtained for observation purpose by rubbing a mineral against by harder surface.

1. It is a reliable property than colour during specific investigation of sulphides and some oxides.
2. Magnetite and chromite, though look alike (inform, colour and luster) can be distinguished from streak. Magnetite gives black streak, whereas chromite gives brown streak.

LUSTRE: Lustre is the nature of shining on the surface of the mineral.

Based on the Quality of Shining Lustre are grouped as:

Sr No	Name of the Lustre	Description of Lustre	Mineral Examples
1	Metallic Lustre	Metallic Lustre is the type of shinning that appears on the surface of a metal	Galena, Pyrite, Gold, Bernie
2	Submetallic Lustre	Similar to Metallic Lustre but the amount of Shining is less	Hematite, Chromite, Magnetite, Ilmenite, Psiolmelane
3	Vitreous Lustre	Shining like a Glass Sheet	Quartz, Calcite, Dolomite, Feldspar barytes etc.
4	Sub vitreous	Sub vitreous Lustre is similar to vitreous but with less shining	Pyroxenes and amphiboles
5	Pearly Lustre	Shining like a Pearl	Tale, Selenite (Gypsum) Mica Muscovite
6	Silkey Lustre	Shining like a Silk	Fibrous Minerals kike asbestos and satinspar
7	Resinous Lustre	Shining like a Resin	Opal agate chalcedony
8	Greasy Lustre	Shining like a Grease	Graphite, Serpentine
9	Adamantine Lustre	Shining like a Diamond	Garnet, Sphene, Zircon Diamond
10	Earthy or Dull Lustre	Shining like a Earth or Chalk	Magnesite, Kaolin, Chalk Bauxite

The Lustre of mineral may be of different degrees of intensity, according to the amount of light reflected form their surfaces: Splendent, Shinning, Glistening Glimmering and Dull.

FRACTURE: Fracture is the randomly broken surface a mineral. It is important to note the characters of the fracture displayed in the broken or chipped surfaces. Fracture with irregular surfaces are independent and different from smooth flat surfaces of cleavages.

Fracture is described as:

Sr No	Name of the Fracture	Description of the Mineral	Mineral Examples
1	Even Fracture	If the broken surface of a mineral is plain an smooth, it is called Even Fracture	Magnetite, Chalk
2	Uneven Fracture	If the broken surface is rough or irregular it is called Uneven Fracture	Most of the Minerals
3	Hackly Fracture	If the broken surface is very irregular like the end of a broken stick	Asbestos, Tremolite, Kyanite
4	Conchoidal Fracture	If the broken surface is smooth and curved it is called Conchoidal Fracture	Opal, Volcanic Glass
5	Sub-Conchoidal Fracture	If the curved nature is less prominent it is called Sub-Conchoidal Fracture	Agate, Flint, Japer etc.

Like streak it is also less useful in mineral identification because a majority of the minerals shows the same kind of Fracture.

CLEAVAGE: The definite direction or plane along which mineral tends to break easily is called the cleavage that mineral. Cleavage pane represents he planes of weakness in the atomic structure of a mineral. Cleavage if present occurs as innumerable parallel planes along which the mineral is equally weak. Hence all such parallel planes of weakness are referred to as a se. depending on their atomic structure. Crystalline mineral will have one set of cleavage, two sets of cleavage ,three sets of cleavage, four sets of cleavage, and six sets of cleavage. The atomic structure of a mineral is definite. The cleavage, character of the mineral will also be definite. In any mineral the occurrence of cleavage can be detected easily by fitting or turning the specimen in different directions. Depending or the atomic structure development of cleavage character may differ in different minerals or in the same mineral.Depending on the degree of perfection cleavage may be described as perfect or eminent or Excellent, Good, Imperfect, Poor or Indistinct.

Changes Angles in

• Calcite
• Pyroxene and Amphibole:

Sr No	Cleavage Sets	Mineral Example
1	One Set	Mica, Chlorite.
2	Two Sets	Feldspar, Pyroxenes, Amphiboles
3	Three Sets	Calcite, Dolomite Galena
4	Four Sets	Fluorite
5	Seven Sets	Sphalerite
6	No Cleavage	Quartz, Divine, Garnet

HARDNESS: Hardness may be defined as the resistance offered by mineral to abrasion or scratching. Hardness may be tested by rubbing or scratching the specimen over a file or knife. The amount powder and the degree of noise produced is a test of the hardness of the mineral. When a softer mineral is scratched by a harder mineral, a definite scratch is observed on the softer mineral.

A standard set of 10 reference mineral is used to determine the hardness of a mineral. This is called Moh's Scale of hardness.

reference	Scale	reference	Scale
Talc	1	Feldspar	6
Gypsum	2	Quartz	7
Calcite	3	Topaz	8
Fluorite	4	Corundum	9
Apatite	5	Diamond	10

Hardness may be tested by means of Penknife (H=6) Window Glass (H=5) and Fingernail (H=2.5).

SPECIFIC GRAVITY OR DENSITY:

Measure of Minerals Density

1. Density = Mass per unit volume Grams / cm3.
2. Density depends on the type of atoms composing the mineral and how densely they have packed by the crystal lattice.

General Range of Density:

1. Density around 2.7 common for light coloured rock forming minerals such as Felds par.
2. Density around 6 common pyrite and other are forming minerals.

Note: Some important rock forming minerals such as pyroxenes and Amphiboles have densities around 3.3.

Specific Gravity is the ratio between its weight and the weight of an equal volume of water at 40°C. Based on the Specific Gravity of Minerals, the Density of Minerals may be described as High, Medium and Low.

Sr No.	Density Mineral	Example
1	Low Density	GYPSUM (2.3) Graphite (2-2.3) Coal (1-1.8)
2	Medium Density (Sp.Gravity 2.5-3.5)	Quartz (2.7), Feldspar (2.56-3.00), Pyroxene (3.1-3.5),Amphiboles (2.9-3.47), Mica (2.7-3.1)
3	High Density (Sp.Gravity 2.5-3.5)	Magnesite (5.18), Hematite (4.9-5.3),Galena (7.5), Hematite (3.5-5.5)Pyrolusite (4.8), Chromite (4.5-4.8) tin stone (8.71)

DEGREE OF TRANSPARENCY:

Depending upon the resistance offered by the mineral to the passage of light through them, they may be classified as transparent, translucent and opaque.

• Transparent: Passage of light through the mineral.
• Translucent: Allows the passage of light but reflects back the light by mineral.
• Opaque: Does not allow and does not reflect back the light.

SPECIAL PROPERTIES:

Some minerals exhibit peculiar characters which enable them to be identified easily. In some cases they are the consequences of the physical properties of the mineral itself. They are as follows.

• Tale by virtue of its Soft Nature (H-1) exhibits smooth touch or soapy feel.
• Graphite -> its low hardness (H-1 to 2) and black color marks on paper and due to their softness and black colour soil the fingers.