Lesson 3.1: Rock-Forming Minerals

Minerals are the building blocks of rocks. Geologists define minerals as?

any present inorganic solids that possess an orderly crystalline structure and a well-defined chemical composition.

Minerals exhibit the following characteristics:

Naturally Occurring, Inorganic, orderly Crystalline Structure, Solid, Defininite Chemiscal Composition

Naturally occurring:

Minerals form through natural processes, including volcanic eruptions, precipitation of a solid out of a liquid, and weathering of pre-existing minerals. Synthetic diamonds and rubies, and other substances with a specific chemical composition and structure produced by chemists, engineers, and manufacturers are not considered true minerals.

Solid:

A true mineral must be solid at temperatures encountered at the earth’s surface. Liquids and gases are not considered minerals, they do not have a characteristic crystal structure. Ice for example ceases to exist as a mineral upon melting into liquid water.

Inorganic processes:

Any material produced through organic activity – such as leaves, bones, peat, shell, or soft animal tissue – is not considered a mineral. Most fossils, although they were once living, have generally had their living tissues completely replaced by inorganic processes after burial; thus, they are considered to be composed of minerals as well.

Chemical composition:

Most minerals exist as chemical compounds composed of two or more elements. The chemical formula of salt, or halite, is NaCl.

Orderly crystalline structure:

Minerals are crystalline substance which means the chemical composition of a mineral is reflected internally in a regular, repeating arrangement of atoms, called the crystal structure of the mineral.

Minerals

are the building blocks of rocks

What are the physical properties of a mineral?

Luster, Hardness, Crystal form/habit, Color, Streak, Cleavage, Specific Gravity

Luster

it is the quality and intensity of reflected light exhibited by the mineral. A. Metallic and B. Non-metallic

Metallic

generally opaque and exhibit a resplended shine similar to a polished metal

Non-metallic

vitreous(glassy), adamantine(brilliant/diamond like), resinous, silky, pearly, dull(earth) greasy among others

Hardness

it is a measure of the resistance of a mineral ( not specific surface ) to abrasion

Crystal Form/Habit

the external shape of a crystal displayed observed as these crystals grow in open spaces

Amorphous

a mineral that do not have a crystal structure

Color

A lot of minerals can exhibit same or similar colors. Individual minerals can also display variety of colors resulting from impurities and also from some geologic processes like weathering.

b. Examples of coloring: quartz can be pink (rose quartz), purple (amethyst), orange

(citrine), white (colorless quartz) etc.

Streak

mineral's color in powdered form. It is inherent in almost every mineral, and is a more diagnostic property compared to color. d. Examples of streak: pyrite (FeS2) exhibits gold color but has a black or dark gray streak.

Cleavage

the property of some minerals to break along specific planes of weakness to form smooth, flat surfaces. Although both are dictated by crystal structure, crystal habit forms as the mineral is growing, relying on how the individual atoms in the crystal come together. Cleavage, meanwhile, is the weak plane that developed after the crystal is formed.

Fracture

Some minerals may not have cleavages but exhibit broken surfaces that are irregular and non-planar. Quartz for example has an inherent weakness in the crystal structure that is not planar. Examples of fracture are conchoidal, fibrous, hackly, and uneven among others.

6. Specific gravity

The ratio of the density of the mineral and the density of water. This parameter indicates how many times more the mineral weighs compared to an equal amount of water. Most silicate, or rock-forming, minerals have specific gravities of 2.6 to 3.4; the ore minerals are usually heavier, with specific gravities of 5 to eight. If you compare similar-sized samples of two different minerals, the one with the higher specific gravity will feel the heaviest; it has a greater heft. For most minerals, relative density isn't a very noteworthy feature, except for some, high relative density is distinctive (examples are barite and galena). The average specific gravity for mineral is around 2.7.

Transparency or diaphaneity

It indicates the extent of light that can pass through the mineral. Hence, the degree of

transparency may depend on the thickness of the mineral.

Magnetism

Indicates the ability of a mineral to attract or repel other minerals.

Tenacity

Is the level of resistance or reaction of minerals to stress such as

crushing, bending, breaking, or tearing.

Brittleness

a mineral turns into powder

• Malleability

a mineral can be flattened by pounding with a hammer.

Ductility

A mineral can be stretched into wire.

Flexible but inelastic

Minerals are bent but they remain in the new position.

Flexible and elastic

Minerals are bent, and they bring back to their original position.

Sectility

ability of minerals to be sliced by a knife.

What are the other properties of a mineral?

transparency or diaphaneity, Magnetism, Tenacity, Britleness, Malleability, Ductility, Flexible but inelastic, sectility, taste and odor.

What are the chemical properties of a mineral?

Chemical properties of minerals show the presence and arrangement of atoms in minerals. Using their chemical properties, minerals are identified by how they react to certain substances. Some minerals, especially carbonate minerals, react visibly with acid. (Usually, a dilute hydrochloric acid [HCl] is used.) When a drop of dilute hydrochloric acid is placed on calcite, it readily bubbles or effervesces, releasing carbon dioxide. Some are toxic like cinnabar and soluble in water like halite.

Classification of Mineral

Native Elements, Silicates, Oxides, Sulfides, Sulfates, Halides, Carbonates, Phosphates, Mineraloid